coalesce (v.)

in Latin, the form of com- "together, with" in compounds with stems beginning in vowels, h-, and gn-; see com-. Taken in English from 17c. as a living prefix meaning "together, mutually, in common," and used promiscuously with native words (co-worker) and Latin-derived words not beginning with vowels (codependent), including some already having it (co-conspirator).

1610s, "the growing together of parts," from French coalition (1540s), from Late Latin coalitus "fellowship," originally past participle of Latin coalescere "unite, grow together, become one in growth" (see coalesce). Political sense, "voluntary temporary union of persons, parties, nations, etc., for the attainment of a certain object" is attested by 1715.