c. 1500, "to loll idly, act or rest lazily and indifferently, move indolently if at all," Scottish, a word of uncertain origin. Meaning "recline lazily" is from 1746. Perhaps [Barnhart] it is from French s'allonger (paresseusement) "to lounge about, lie at full length," from Old French alongier "lengthen," from Latin longus "long" (see long (adj.)).
Another etymology traces it through the obsolete noun lungis "slow, lazy person" (c. 1560), which is from French longis "an idle, stupid dreamer," a special application, for some obscure reason, in Old French of the proper name Longis, which is from Latin Longius, Longinus. In old mystery plays and apocryphal gospels, Longinus is the name of the centurion who pierces Christ's side with a spear; the name perhaps was suggested by Greek longe "a lance" in John xix.34. But popular etymology associated the name directly with long (adj.). Related: Lounged; lounging; lounger.
1806 as "act of lounging;" 1830 as "couch on which one can lie at full length;" 1881 as "comfortable drawing room" (suitable for lounging); from lounge (v.). Earlier senses, now out of use, were "pastime" (1788), "place for gathering" (1775). Lounge lizard is by 1917, perhaps 1912, originally in reference to men who loitered in tea rooms to flirt.