What is the X in X-mas?
"class, sort, variety," from Old English gecynd "kind, nature, race," related to cynn "family" (see kin), from Proto-Germanic *gakundjaz "family, race" (see kind (adj.)). 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.). Other earlier, now obsolete, senses in English included "character, quality derived from birth" and "manner or way natural or proper to anyone." Use in phrase a kind of (1590s) led to colloquial extension as adverb (1804) in phrases such as kind of stupid ("a kind of stupid (person)").
"friendly, deliberately doing good to others," from Old English gecynde "natural, native, innate," originally "with the feeling of relatives for each other," from Proto-Germanic *gakundiz "natural, native," from *kunjam (see kin), with collective prefix *ga- and abstract suffix *-iz. Sense development from "with natural feelings," to "well-disposed" (c.1300), "benign, compassionate" (c.1300).