Old English lust "desire, appetite, pleasure," from Proto-Germanic *lustuz (cf. Old Saxon, Old Frisian, Dutch, German lust, Old Norse lyst, Gothic lustus "pleasure, desire, lust"), from PIE *las- "to be eager, wanton, or unruly" (cf. Latin lascivus "wanton, playful, lustful;" see lascivious).
In Middle English, "any source of pleasure or delight," also "an appetite," also "a liking for a person," also "fertility" (of soil). Sense of "sinful sexual desire, degrading animal passion" (now the main meaning) developed in late Old English from the word's use in Bible translations (e.g. lusts of the flesh to render Latin concupiscentia carnis [I John ii:16]); the cognate words in other Germanic languages tend still to mean simply "pleasure."