CO
Abbreviation with 12 meanings
| Stands for | Colorado |
|---|---|
| Meanings | 12 |
| Categories | Geography & Places, Science & Engineering, Business & Finance, Military, Medical, Law & Legal |
| Also written | Co, Co. |
CO has 12 meanings. The most common are Colorado (US state) and Carbon monoxide (chemistry); it can also stand for Company, Commanding officer, Colombia, County and Cobalt, plus 5 more listed below.
Meanings of CO at a glance
| # | CO stands for | Context |
|---|---|---|
| 1 | Colorado | Geography & Places › US State |
| 2 | Carbon monoxide | Science & Engineering › Chemistry |
| 3 | Company | Business & Finance › Company Type |
| 4 | Commanding officer | Military › Military Term |
| 5 | Colombia | Geography & Places › Country Code |
| 6 | County | Geography & Places › Geographic Feature |
| 7 | Cobalt | Science & Engineering › Chemical Element |
| 8 | Cardiac output | Medical › Cardiology |
| 9 | Certificate of occupancy | Business & Finance › Real Estate & Mortgage |
| 10 | Certificate of origin | Business & Finance › Logistics, Supply Chain & Trade |
| 11 | Change order | Business & Finance › Project Management |
| 12 | Correctional officer | Law & Legal › Criminal Law |
1. Colorado
Geography & Places · US State Abbreviations
Admitted on August 1, 1876, a month after the nation's 100th birthday, which gives Colorado its Centennial State nickname. Denver, the capital, has a step on its Capitol marked exactly one mile above sea level, and the state contains more than 50 peaks above 14,000 feet.
Example: Trailhead parking in Leadville, CO fills by 6 a.m. on summer weekends.
Colo. is the AP and traditional form; the older Col. was dropped because it collides with colonel and column. The code CO came with the 1963 list. Internationally CO is Colombia's ISO code and the .co domain, and in chemistry it is carbon monoxide, so check the context; Colorado is never CL or CR.
2. Carbon monoxide
Science & Engineering · Chemistry Abbreviations
Colorless, odorless, toxic gas formed by incomplete combustion in furnaces, generators, vehicles and charcoal grills. It binds to hemoglobin more than 200 times more tightly than oxygen, starving tissues of oxygen, and is a leading cause of accidental poisoning, which is why CO alarms are required in many homes.
Example: The CO detector went off at 3 a.m., and firefighters traced the leak to a cracked furnace heat exchanger.
Early symptoms, including headache, dizziness and nausea, resemble flu, so poisoning is often missed. Industrially, carbon monoxide combined with hydrogen as syngas is a major feedstock for methanol and synthetic fuels. Capitalization matters: CO is carbon monoxide, while Co is the element cobalt.
3. Company (Co.)
Business & Finance · Company Type Abbreviations · also used in the military
Abbreviation of company used in business names, either as a standalone ending, as in "Ford Motor Co.," or combined with another designation, as in "Co., Ltd." In many US states "Company" or "Co." is an acceptable ending for a corporation's legal name.
Example: The Coca-Cola Co. reported higher sales of zero-sugar drinks in its quarterly results.
"Co." alone does not always indicate limited liability; partnerships and sole proprietors have long used "& Co." in trading names, as in older banking houses. In Asian English-language company names, "Co., Ltd." is the standard form for limited companies. Pronounced "co" or "company."
4. Commanding officer
Military · Military Term Abbreviations
Officer in command of a military unit, ship, squadron or installation, legally responsible for everything the unit does or fails to do. In the Navy and Marine Corps, the CO of a ship is called "Captain" regardless of rank.
Example: The CO ordered the ship to general quarters when the drone was detected.
The Army more often says "commander," while the Navy and Marine Corps say "commanding officer" or CO. Navy commanding officers can be relieved for "loss of confidence," a frequent headline after collisions or misconduct. In unit designations, Co means company, and CO is also the postal code for Colorado.
5. Colombia
Geography & Places · Country Code Abbreviations
Colombia, capital Bogotá, alpha-3 COL, has marketed its .co domain worldwide since 2010 as short for company, and services such as Twitter's t.co link shortener made the ending familiar.
Example: The startup chose a .co domain because the .com was taken, unaware it belongs to Colombia.
In US addresses CO is Colorado, and in chemistry CO is carbon monoxide. Colombia is often misspelled Columbia, the name of the US river, university and district.
6. County (Co.)
Geography & Places · Geographic Feature Abbreviations
Abbreviation of County in place names and addresses, as in Orange Co., California, or Co. Cork in Ireland, where the word precedes the name.
Example: The farmhouse is near Kinsale, Co. Cork, about 30 minutes from the airport.
Irish addresses traditionally include the county as Co. Kerry or Co. Clare. In US prose County is usually spelled out. Co. more often means Company in business names.
7. Cobalt (Co)
Science & Engineering · Chemical Element Abbreviations
A hard, magnetic transition metal with atomic number 27, cobalt is a key ingredient of lithium-ion battery cathodes, heat-resistant superalloys for jet engines, and the deep blue pigment used in glass and ceramics. Vitamin B12 contains a cobalt atom, and the isotope cobalt-60 is used to sterilize medical supplies.
Example: The cathode chemistry is NMC 811, with Ni, Mn and Co in an 8:1:1 ratio.
Swedish chemist Georg Brandt isolated cobalt around 1735, the first metal discovered since ancient times. Its name comes from German Kobold, a mischievous goblin; miners blamed kobolds for ores that looked valuable but released poisonous arsenic fumes when smelted. Capitalization matters: Co is cobalt, while CO (two capitals) is carbon monoxide.
8. Cardiac output
Medical · Cardiology Abbreviations
Volume of blood pumped by the heart per minute, the product of heart rate and stroke volume, normally about 4 to 8 liters per minute at rest in adults. It is measured by thermodilution or the Fick method during right heart catheterization, or estimated by echocardiography and noninvasive monitors.
Example: Thermodilution CO 2.8 L/min with CI 1.6: low-output state, start dobutamine.
Low cardiac output with high filling pressures defines cardiogenic shock, while septic shock typically shows high output with low vascular resistance. The Fick principle, described by Adolf Fick in 1870, calculates output from oxygen consumption and the arteriovenous oxygen difference. In toxicology CO means carbon monoxide.
9. Certificate of occupancy
Business & Finance · Real Estate & Mortgage Abbreviations
Document issued by a local building department confirming that a new building, conversion or major renovation complies with building codes and may legally be occupied for a specific use.
Example: The tenants can't move in until the city issues the CO.
Lenders and buyers check for a CO when buying new construction or converted buildings. A temporary certificate of occupancy (TCO) may allow use while minor work is finished.
10. Certificate of origin
Business & Finance · Logistics, Supply Chain & Trade Abbreviations
Document certifying the country in which goods were manufactured, required by some importing countries and used to claim reduced duties under free trade agreements. Non-preferential certificates are often issued by chambers of commerce.
Example: The buyer in Egypt needs a chamber-stamped CO with the shipment.
Preferential origin may be shown with special forms or self-certification statements depending on the agreement, such as USMCA certifications in North America. Origin is determined by rules such as "substantial transformation," not simply where goods shipped from. In real estate, CO means certificate of occupancy.
11. Change order
Business & Finance · Project Management Abbreviations
Written amendment to a construction or fixed-price contract, agreed by owner and contractor, that changes the scope of work and adjusts the contract price, schedule or both.
Example: The owner's request for upgraded windows added a $38,000 CO.
In US construction, the American Institute of Architects' G701 form is a widely used change order document. Frequent change orders are a leading cause of construction disputes.
12. Correctional officer
Law & Legal · Criminal Law Abbreviations
Officer who maintains security and order in a prison or jail, supervising inmates, conducting counts and searches and responding to incidents. The title has largely replaced the older word "guard" in official usage.
Example: Two COs were injured breaking up the fight in the housing unit.
Correctional officers employed by the federal Bureau of Prisons are federal law enforcement officers. Severe staffing shortages in many state systems have led to lockdowns and mandatory overtime. CO also means commanding officer in the military and carbon monoxide in science.
Related abbreviations
More US state abbreviations
- AL – Alabama
- AR – Arkansas
- AZ – Arizona
- CA – California
- CT – Connecticut
- DC – District of Columbia
- DE – Delaware
- FL – Florida
See all 51 US state abbreviations →
More chemistry abbreviations
- BPA – Bisphenol A
- CAS – Chemical Abstracts Service
- CFC – Chlorofluorocarbon
- CH4 – Methane
- CO2 – Carbon dioxide
- conc. – Concentrated
- DCM – Dichloromethane
- DDT – Dichlorodiphenyltrichloroethane
See all 106 chemistry abbreviations →
This entry is for general education and is not medical or legal advice. Abbreviation use varies between institutions; always confirm in context.