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Old English hleo "shelter, cover, defense, protection," from Proto-Germanic *khlewaz (cf. Old Norse hle, Danish læ, Old Saxon hleo, Dutch lij "lee, shelter"). No known cognates outside Germanic; original sense uncertain and might have been "warm" (cf. German lau "tepid," Old Norse hly "shelter, warmth"), which might link it to PIE *kele- (1) "warm." As an adjective, 1510s, from the noun.