mid-12c., "large group of people," from Old French compagnie "society, friendship, intimacy; body of soldiers" (12c.), from Late Latin companio, literally "bread fellow, messmate," from Latin com "with, together" (see com-) + panis "bread," from PIE root *pa- "to feed." Abbreviation co. dates from 1670s.
Meaning "companionship, consort of persons one with another, intimate association" is from late 13c. Meaning "person or persons associated with another in any way" is from c. 1300. In Middle English the word also could mean "sexual union, intercourse" (c. 1300).
From late 14c. as "a number of persons united to perform or carry out anything jointly," which developed a commercial sense of "business association" by 1550s, the word having been used in reference to trade guilds from late 14c. Meaning "subdivision of an infantry regiment" (in 19c. usually 60 to 100 men, commanded by a captain) is from c. 1400.
Meaning "person or persons with whom one voluntarily associates" is from c. 1600; phrase keep company "consort" is from 1560s (bear company in the same sense is from c. 1300). Expression two's company "two persons are just right" (for conversation, etc.), is attested from 1849; the following line varies: but three is none (or not), 1849; three's trumpery (1864); three's a crowd (1856).
1550s, "engagement to marry," a variant of ensurance "an assurance, pledge, guarantee," from Old French enseurance "assurance," from ensurer, from en- "make" (see en- (1)) + sur "safe, secure, undoubted" (see sure (adj.)).
"involving or characterized by prudence," mid-15c., prudencial, from Medieval Latin prudentialis, from Latin prudentia "a foreseeing, foresight" (see prudence). Related: Prudentially.
Prudential, the U.S. insurance company, dates to the 1870s; its logo featuring the Rock of Gibraltar dates from c. 1900 and was widely known 20c. The Prudential of Great Britain is a different company, founded 1848 to provide loans to professional and working people, noted for its door-to-door agents ("the Man from the Pru").
1610s, "subscriber," agent noun from underwrite (v.). Insurance sense is from 1620s.
Old English underwritan "write at the foot of; subscribe;" see under + write (v.). A loan-translation of Latin subscribere (see subscribe). Used literally at first; modern sense of "to accept the risk of insurance" (1620s) is from notion of signing a marine insurance policy. Meaning "to support by a guarantee of money" is recorded from 1890.
1825, "company, band," especially of performers, actors, dancers, etc., from French troupe "company" (see troop (n.)).
also preexisting, 1590s, present-participle adjective from pre-exist. The medical insurance pre-existing condition is attested from 1942.