mid-13c. "that which is given" (c. 1100 in surnames), from a Scandinavian source such as Old Norse gift, gipt "gift; good luck," from Proto-Germanic *geftiz (source also of Old Saxon gift, Old Frisian jefte, Middle Dutch ghifte "gift," German Mitgift "dowry"), from *geb- "to give," from PIE root *ghabh- "to give or receive." For German Gift, Dutch, Danish, Swedish gift "poison," see poison (n.).
Sense of "natural talent" (regarded as conferred) is from c. 1300, perhaps from earlier sense of "inspiration, power miraculously bestowed" (late 12c.), as in the Biblical gift of tongues. Old English cognate gift is recorded only in the sense "bride-price, marriage gift (by the groom), dowry" (hence gifta (pl.) "a marriage, nuptials"). The Old English noun for "a giving, gift" was giefu, which is related to the Old Norse word. Sense of "natural talent" is c. 1300, perhaps from earlier sense of "inspiration" (late 12c.). The proverbial gift horse was earlier given horse:
No man ought to looke a geuen hors in the mouth. [Heywood, 1546]
The modern form perhaps traces to Butler's "Hudibras" (1663), where the tight iambic tetrameter required a shorter phrase:
He ne'er consider'd it, as loth
To look a Gift-horse in the mouth.