co
co — prefix
1. a prefix added to the start of a word to show that two or more people do somethi
a prefix added to the start of a word to show that two or more people do something together, or that someone shares a role or position with another person
Tuan co-founded a language school with two old classmates after they graduated.
co- + verb: co-found (start something together)
The co-authors of the science paper shared the prize money equally between them.
co- + noun: co-author (joint creator)
Kofi and his uncle are co-owners of a small carpentry workshop in Kumasi.
Ravindra was named co-chair of the neighbourhood safety group last Tuesday.
The two film studios agreed to co-produce a documentary about sea turtles.
- co-author a book
- co-own a business
- co-chair a committee
- co-produce a film
- co-star in a movie
Usage Note
Added to nouns, verbs, and adjectives. Most often used with nouns that name a role or job (co-pilot, co-star, co-director). The hyphen is usually kept in British English; American English sometimes writes the word without it.
Common Mistakes
co — noun
1. a written short form of the word 'company', placed after the name of a business
a written short form of the word 'company', placed after the name of a business
Liang started working at Norton & Co., a small accounting firm, last month.
& Co. in formal business names
The letter was addressed to Patel & Co., 42 High Street, Leicester.
Emma's grandfather founded Brown & Co. back in 1963, selling farming tools.
Cole got a job offer from a law firm called Dawson & Co. this morning.
The shop sign read 'H. Martin & Co. — Fine Tailoring Since 1887'.
- Smith & Co.
- Jones & Co.
- Brown & Co.
Usage Note
Always written with a capital C followed by a period. Used mainly in formal or traditional business names, especially in the UK. Not used as a standalone word for any company.
Common Mistakes
2. a written short form of the word 'county', placed before the name of a county, u
a written short form of the word 'county', placed before the name of a county, used mainly in Ireland and parts of the UK
Madison's relatives moved to Co. Clare, a quiet area on Ireland's west coast.
Co. + county name in Irish addresses
The road sign read 'Co. Durham' as they drove north from Yorkshire.
Hugo traced his ancestors back to a tiny village in Co. Cork, Ireland.
The old census records for Co. Kerry were stored in the national archive in Dublin.
A postcard arrived from Co. Galway, where the family was spending the summer.
- Co. Dublin
- Co. Cork
- Co. Clare
- Co. Galway
Usage Note
Always written with a capital C followed by a period. Most commonly seen in Irish place names (Co. Dublin, Co. Cork). Not used for US or Canadian counties.
Common Mistakes
3. a short form for Commanding Officer, meaning the senior officer who leads a mili
a short form for Commanding Officer, meaning the senior officer who leads a military unit or base
The CO ordered all personnel to gather in the main hall by 0600 hours.
CO as subject followed by a military command verb
Karim received a formal commendation from the CO for his quick thinking during the drill.
The new CO introduced himself to every soldier in the unit last Monday.
A photograph of the former CO hung in the corridor outside the briefing room.
The CO walked into the mess hall and the room fell completely silent.
- the new CO
- report to the CO
- the former CO
Usage Note
Always written in capital letters without periods (CO, not C.O.). Used in spoken military English as well as in writing — pronounced as the two letters 'C-O'.
Common Mistakes
4. the two-letter postal code for the western American state of Colorado, placed af
the two-letter postal code for the western American state of Colorado, placed after a city name in addresses and on forms
The package was sent to Boulder, CO, but took three extra days to arrive.
City, CO format in US postal addresses
Lukas drove from Denver, CO, all the way to Santa Fe in a single day.
Noa wrote her address as 242 Pine Street, Aspen, CO 81611, on the form.
The hiking festival will be held in Colorado Springs, CO, at the end of July.
Felipe's cousin lives in a small mountain town near Durango, CO, in the southwest.
- Denver, CO
- Boulder, CO
- Colorado Springs, CO
Usage Note
Always written in capital letters without periods. One of the fifty US state codes used by the postal service. Do not confuse with CO meaning Commanding Officer.
Common Mistakes
co — symbol
1. the chemical symbol for cobalt, a hard, shiny, silver-grey metal that is used in
the chemical symbol for cobalt, a hard, shiny, silver-grey metal that is used in batteries, magnets, and strong metal mixtures
The phone battery contains Co, a metal mined mostly in central Africa.
Co as chemical element symbol in scientific writing
Engineers are trying to make batteries that need less Co than current models.
The supplement label listed Co among the trace minerals in each tablet.
The periodic table places Co between iron and nickel in the ninth group.
Co is mixed with other metals to make aircraft parts that resist high heat.
- Co content
- Co mining
- Co supply
Usage Note
Always written with a capital C followed by a lowercase o. Used mainly in chemistry, materials science, and industry. Do not confuse with CO (Commanding Officer) or CO (Colorado).