From Middle English pal, palle, from Old English pæl, pæll, from Old French paile and Latin pallium ("cloak; covering") (and thus a pallium), probably from palla (possibly from Proto-Indo-European *pel- ("to cover, wrap; hide, skin; cloth")) + -ium.
Formed by aphesis from appal, appall, possibly under the influence of the figurative meaning of the unrelated noun pall.
Alternatively, the word may be derived from Middle English pallen ("to diminish, impair, weaken; to become faint; to lose spirit"), formed by aphesis from apallen, from palleō (ultimately from Proto-Indo-European *pel-, *pelH-) + -idus.