diminutive suffix, first attested late 12c. in proper names adopted from Flanders and Holland. As it is not found in Old English it probably is from Middle Dutch -kin, properly a double-diminutive, from -k + -in. Equivalent to German -chen. Also borrowed in Old French as -quin, where it usually has a bad sense.
This suffix, which is almost barren in French, has been more largely developed in the Picard patois, which uses it for new forms, such as verquin, a shabby little glass (verre); painequin, a bad little loaf (pain); Pierrequin poor little Pierre, &c. ["An Etymological Dictionary of the French Language," transl. G.W. Kitchin, Oxford, 1878]
Used in later Middle English with common nouns. In some words it is directly from Dutch or Flemish.
c. 1200, from Old English cynn "family; race; kind, sort, rank; nature" (also "gender, sex," a sense obsolete since Middle English), from Proto-Germanic *kunja- "family" (source also of Old Frisian kenn, Old Saxon kunni "kin, kind, race, tribe," Old Norse kyn, Old High German chunni "kin, race;" Danish kjön, Swedish kön, Middle Dutch, Dutch kunne "sex, gender;" Gothic kuni "family, race," Old Norse kundr "son," German Kind "child"), from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups.
In the Teutonic word, as in Latin genus and Greek [genos], three main senses appear, (1) race or stock, (2) class or kind, (3) gender or sex .... [OED]
Related to both words kind and to child. From 1590s as an adjective, from the noun and as a shortening of akin. Legal next of kin (1540s) does not include the widow, "she being specifically provided for by the law as widow" [Century Dictionary], and must be a blood relation of the deceased.
before vowels, kin-, word-forming element in use from late 19c. and meaning "motion," from Greek kino-, from kinein "to move" (from PIE root *keie- "to set in motion").
also cumquat, 1690s, from Chinese (Cantonese) kamkwat, from kam "golden" + kwat "orange." Said in OED to be a Cantonese dialectal form of Chinese kin-ku.