languor (n.)

c. 1300, "disease, sickness; distress, mental suffering," from Old French langor "sickness; weakness" (12c., Modern French langueur), from Latin languorem (nominative languor) "faintness, feebleness, lassitude," from languere "be weak or faint" (see lax). Sense in English shifted to "faintness, weariness" (1650s) and "habitual want of energy" (1825).