- co-is a prefix of Latin origin, and is used to form words that include the meaning ‘together, in common’. Spelling practice varies with regard to use of a hyphen: some words (especially when the second element begins with a vowel) include it, whereas others are written as one word. The diaeresis (ö) that formerly punctuated words as in coöperate, is now largely disused. Recommended spellings are as follows:coagulate / cofactor / co-optcoalition / cogeneration / coordinateco-author (noun and verb) / cohabit / co-parentcohere / co-partnercoaxial / co-host / co-pilotco-determination / coincide / co-respondent (in divorce case)co-driver / coitionco-education / co-latitude / co-signatory (to an agreement etc.)coefficient / co-occurcoequal / co-occurrence / co-starcoeval / co-op / co-workercoexist / cooperate / uncooperativecoexistent / cooperation / uncoordinatedcoextensive / cooperative
Modern English usage. 2014.