Old English hleo "shelter, cover, defense, protection," from Proto-Germanic *khlewaz (cognates: 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" (compare German lau "tepid," Old Norse hly "shelter, warmth"), which might link it to PIE *kele- (1) "warm." Nautical sense "that part of the hemisphere to which the wind is directed" (c.1400) is from the notion of the side of the ship opposite that which receives the wind as the sheltered side. As an adjective, 1510s, from the noun.