n.1 lack of energy or vitality; a torpid, inert, or apathetic state.
2 Med. morbid drowsiness or prolonged and unnatural sleep.
Derivatives:
lethargic adj. lethargically adv.
Etymology: ME f. OF litargie f. LL lethargia f. Gk lethargia f. lethargos forgetful f. leth-, lanthanomai forget