co.

IPA/kˈəʊ/
KK[kˈo]IPA/kˈoʊ/

co. — abbreviation

1. short way of writing 'company' in the name of a business, usually placed after a

1.abbreviationB1
Definition

short way of writing 'company' in the name of a business, usually placed after a personal or family name and an ampersand

Example

The sign above the shop read Tunde & Co. Tailors in gold paint.

appears after personal name + & in business names

Hari worked as a junior accountant at Patel & Co. for nine years.

Common collocations
  • & Co.
  • and Co.
  • Co. Ltd.
Synonyms
  • Inc.

    American abbreviation for 'Incorporated' — used for limited-liability corporations rather than informal partnerships

  • Ltd.

    British abbreviation for 'Limited' — signals a private limited company structure

Grammar Patterns

written after a business name

Smith & Co.

Usage Note

Only used inside a registered business name; never replaces the word 'company' in running prose. Always followed by a period in American writing; British writing sometimes drops it.

Common Mistakes

I work for a large co.
I work for a large company.
'co.' only appears as part of a fixed business name, not as a general noun for 'company'.

2. short way of writing 'county' before the name of a place, used mostly in Irish a

2.abbreviationB2
Definition

short way of writing 'county' before the name of a place, used mostly in Irish and British postal addresses to mark which county the town belongs to

Example

Élise mailed the parcel to her cousin in Killarney, Co. Kerry, last Friday.

appears before an Irish county name in addresses

Minho rented a small farmhouse in Co. Galway for the summer holiday.

Common collocations
  • Co. Cork
  • Co. Kerry
  • Co. Down
  • Co. Galway
Synonyms
  • Cty.

    alternative American abbreviation, common on US road signs and county-level documents

Grammar Patterns

written before a county name

Co. Cork

Usage Note

Most common in Irish addresses (Co. Cork, Co. Kerry, Co. Down) and on UK historical maps. Distinguish from sense 1 (company) by position — county 'Co.' precedes a place name; company 'Co.' follows a personal name with '&'.

Common Mistakes

I visited Cork Co. last summer.
I visited Co. Cork last summer.
the abbreviation goes before the county name, not after.

3. short way of writing 'Commanding Officer', the person who is in charge of a grou

3.abbreviationB2
Definition

short way of writing 'Commanding Officer', the person who is in charge of a group of soldiers, sailors, or air crew and gives them their orders

Example

Tariq saluted the CO before stepping into the briefing tent at dawn.

everyday in-service usage: salute / report to the CO

Every platoon leader must report any injuries to the CO within two hours.

Common collocations
  • the CO
  • report to the CO
  • salute the CO
Synonyms
  • commander

    general word for any military leader; CO refers specifically to the officer in charge of one unit

  • OC

    British military variant 'Officer Commanding' — used for company-level units rather than battalions

Antonyms
  • XO

    Executive Officer — second-in-command, who reports to the CO

Grammar Patterns

used in military communication and documents

the CO of [unit]

Usage Note

Usually written without periods (CO) in modern military style, though older documents and dictionaries still list it as 'co.' Always takes 'the' before it when referring to a specific officer.

Common Mistakes

A co. visited our base.
A CO visited our base.' / 'The CO visited our base.
military abbreviations of ranks and roles are almost always written in capital letters without a period.

4. two-letter symbol for the US state of Colorado, written after a city name on env

4.abbreviationB2
Definition

two-letter symbol for the US state of Colorado, written after a city name on envelopes and forms so the postal service knows where to deliver

Example

Hannah addressed the birthday card to her grandmother in Boulder, CO.

standard US postal format: city, CO + ZIP code

The shipping label clearly showed Denver, CO 80202 as the delivery point.

Common collocations
  • Denver, CO
  • Boulder, CO
  • Aspen, CO
Synonyms
  • Colo.

    older traditional abbreviation for Colorado, still seen in books published before the 1960s

Grammar Patterns

written after a city name in US postal addresses

Denver, CO 80202

Usage Note

Always written in capital letters as 'CO' (no period) in modern US postal addresses, following the US Postal Service two-letter code system. The period form 'Co.' for Colorado is now rare and appears mostly in older atlases.

Common Mistakes

I live in co.
I live in Colorado.' / 'I live in CO.
the abbreviation is only for addresses and forms, never for general writing about the state.

5. short way of writing 'care of', used on letters and parcels to show that a piece

5.abbreviationB2
Definition

short way of writing 'care of', used on letters and parcels to show that a piece of mail should reach the named person through a different person or address

Example

Sari posted the letter to her brother c/o Mrs. Park at the language school.

commonly written as 'c/o' on the envelope line below the addressee

Please send the documents to me c/o the Tokyo office until further notice.

Common collocations
  • c/o
  • send c/o
  • addressed c/o
Synonyms
  • att.

    abbreviation of 'attention' — directs mail to a person inside an organization, but doesn't imply forwarding through them

  • via

    less formal alternative — 'via my office', shows the path mail takes

Grammar Patterns

written between two addressees on mail

Name, c/o Other Name

Usage Note

Almost always written as 'c/o' rather than 'co.' on real envelopes. Always names a person or organization after it that will pass the mail on to the real recipient. Distinguish from sense 1 — 'c/o' includes a slash and stands BETWEEN two named parties.

Common Mistakes

Send it co. my office.
Send it c/o my office.
when meaning 'care of', the standard form on mail includes a slash between the letters.

6. short way of writing 'conscientious objector', a person who refuses to serve in

6.abbreviationC1
Definition

short way of writing 'conscientious objector', a person who refuses to serve in the army because their religious or moral beliefs are against killing or fighting in war

Example

Eric's grandfather was registered as a CO during the Second World War.

common pattern: registered / classified / known as a CO

The museum displayed letters written by COs who refused to carry weapons in 1942.

Common collocations
  • registered as a CO
  • wartime COs
  • Quaker COs
Synonyms
  • pacifist

    broader term — opposes all war on principle; a CO is the formal legal status for refusing military service

  • draft resister

    American term used during the Vietnam War — refuses to register for the draft, often without claiming religious grounds

Antonyms
  • enlistee

    person who voluntarily joins the military, opposite stance to a CO

Grammar Patterns

used in historical and military records

registered as a CO

Usage Note

Mostly appears in historical writing about the World Wars or in modern conscription debates. The full phrase 'conscientious objector' is preferred in academic and journalistic prose; 'CO' is reserved for archive records and military paperwork.

Common Mistakes

He became a co. for moral reasons.
He became a CO for moral reasons.
when meaning 'conscientious objector', the abbreviation is written in capitals.

Word family

Synonym discussion

Sense: abbreviation/1

These four abbreviations all appear after a personal or family name to mark a business, but each signals a different legal structure. 'Co.' is the oldest and most general — it simply means 'company' and often suggests a small partnership or family firm (Smith & Co.). 'Inc.' is American and stands for 'Incorporated': the business is a registered corporation with shareholders and limited liability. 'Ltd.' is the British equivalent for 'Limited', identifying a private limited company. 'Corp.' is short for 'Corporation' and is also American, suggesting a larger, more formal entity. Choose 'Co.' for traditional or boutique names (Patel & Co. Tailors), 'Inc.' or 'Corp.' for US firms (Apple Inc., Microsoft Corp.), and 'Ltd.' for UK firms (Wilkin & Sons Ltd.).

Co. ↗Inc. ↗Ltd. ↗Corp.

Etymology

English

All six modern meanings of 'co.' are formed by dropping letters from a longer English word. The earliest, 'co.' for 'company', appears in British business records from the 1700s, when ledger writers shortened repeated firm names. 'Co.' for 'county' was standardised by 19th-century postal services in Britain and Ireland for compact addresses. 'CO' as the US two-letter code for Colorado was introduced by the US Postal Service in 1963. The military senses (Commanding Officer; conscientious objector) entered written use in the World War I period as army record-keeping demanded short, regular abbreviations.