Old English clif "steep and rugged face of a rocky mass, promontory, steep slope," from Proto-Germanic *kliban (source also of Old Saxon clif, Old Norse klif, Middle Dutch klippe, Dutch klip, Old High German klep, German Klippe "cliff, promontory, steep rock").
Clift has been a variant spelling since 15c. and was common in early Modern English. It represents an influence by or merger with clift, a variant of cleft (n.). Cliff-dweller first attested 1879, American English, in reference to aboriginal tribes of the U.S. Southwest who built dwellings in natural recesses in cliffs.