"class, sort, variety," from Old English gecynd "kind, nature, race," related to cynn "family" (see kin), from Proto-Germanic *kundjaz "family, race," from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups.
Ælfric's rendition of "the Book of Genesis" into Old English came out gecyndboc. The prefix disappeared 1150-1250. No exact cognates beyond English, but it corresponds to adjective endings such as Goth -kunds, Old High German -kund. Also in English as a suffix (mankind, etc., also compare godcund "divine"). Other earlier, now obsolete, senses included "character, quality derived from birth" and "manner or way natural or proper to anyone."
Phrase a kind of (1590s) indicating something like or similar to something else led to the colloquial extension as adverb (1804) in phrases such as kind of stupid "a kind of stupid (person), (one) not far from stupidity." However "good usage" once condemned as inaccurate the use as an adjective as in our kind of people, some kind of joke. All kinds is Old English alles cynnes, in Middle English sometimes contracted to alkins.
"friendly, deliberately doing good to others," Middle English kinde, from Old English (ge)cynde "natural, native, innate," originally "with the feeling of relatives for each other," from Proto-Germanic *kundi- "natural, native," from *kunjam "family" (see kin), with collective or generalizing prefix *ga- and abstract suffix *-iz. The word rarely appeared in Old English without the prefix, but Old English also had it as a word-forming element -cund "born of, of a particular nature" (see kind (n.)). Sense development probably is from "with natural feelings," to "well-disposed" (c. 1300), "benign, compassionate, loving, full of tenderness" (c. 1300).