1570s, alteration (by influence of cleft, new weak past participle of cleave (v.1)), of Middle English clift "fissure, rift, space or opening made by cleaving" (early 14c.), from Old English geclyft (adj.) "split, cloven," from Proto-Germanic *kluftis (compare Old High German chluft, German Kluft, Danish kløft "cleft, fissure, gap"), from PIE root *gleubh- "to tear apart, cleave." In Middle English anatomy, it meant "the parting of the thighs" (early 14c.).
"split, cloven," late 14c., past-participle adjective from cleave (v.1)). Cleft palate attested from 1828.