early 13c., "a collateral blood relative more remote than a brother or sister" (mid-12c. as a surname), from Old French cosin "nephew; kinsman; cousin" (12c., Modern French cousin), from Latin consobrinus "cousin," originally "mother's sister's son," from assimilated form of com "with, together" (see com-) + sobrinus (earlier *sosrinos) "cousin on mother's side," from soror (genitive sororis) "sister" (see sister).
Specific modern usage, "the son or daughter of an uncle or aunt," is attested by c. 1300, but throughout Middle English the word also was used of grandchildren, godchildren, etc. Extended sense of "closely related thing" is from late 14c.
Italian cugino, Danish kusine, Polish kuzyn also are from French. German vetter is from Old High German fetiro "uncle," perhaps on the notion of "child of uncle." Words for cousin tend to drift to "nephew" on the notion of "father's nephew."
Many IE languages (including Irish, Sanskrit, Slavic, and some of the Germanic tongues) have or had separate words for some or all of the eight possible "cousin" relationships, such as Latin, which along with consobrinus had consobrina "mother's sister's daughter," patruelis "father's brother's son," atruelis "mother's brother's son," amitinus "father's sister's son," etc. Old English distinguished fæderan sunu "father's brother's son," modrigan sunu "mother's sister's son," etc.
Used familiarly as a term of address since early 15c., especially in Cornwall. Phrase kissing cousin is a Southern U.S. expression, 1940s, apparently denoting "those close enough to be kissed in salutation;" Kentish cousin (1796) is an old British term for "distant relative." For cousin german "first cousin" (early 14c.) see german (adj.).
"to cheat, defraud," 1560s, of uncertain origin; perhaps from French cousiner "cheat on pretext of being a cousin;" or from Middle English cosyn "fraud, trickery" (mid-15c.), which is perhaps related to Old French coçon "dealer, merchant, trader," from Latin cocionem "horse dealer." Related: Cozened; cozening; cozenage.
"distant in relationship" (by some expressed degree, for example first cousin once removed), 1540s, from past participle of remove (v.). Meaning "remote, separated, secluded" from something is from 1610s.
"of the same parents or grandparents," c. 1300, from Old French germain "own, full; born of the same mother and father; closely related" (12c.), from Latin germanus "full, own (of brothers and sisters); one's own brother; genuine, real, actual, true," related to germen (genitive germinis) "sprout, bud," which is of uncertain origin; perhaps it is a dissimilation of PIE *gen(e)-men-, suffixed form of root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups.
Your cousin-german (also first cousin) is the son or daughter of an uncle or aunt; your children and your first cousins are second cousins to one another; to you, your first cousin's children are first cousins once removed.
1867, Dundreary whiskers, long, bushy sideburns without a beard, resembling those worn by actor E.A. Sothern (1826-1881) while playing Lord Dundreary, the witless, indolent character in English dramatist Tom Taylor's play "Our American Cousin" (1858).