Lewis & Short

† lēthargus, a, um, adj., Gr. λήθαργος, drowsy, lethargic: morbus, Plin. 23, 1, 6, § 10; Schol. Juv. 6, 613.
Esp. as subst.

  1. A. lēthargus, i, m. (sc. morbus), drowsiness, lethargy (in Cels. 3, 20, written as Greek): lethargo grandi est oppressus, Hor. S. 2, 3, 145; cf.: gravi lethargo oppressus, Serv. Sulp. ap. Quint. 4, 2, 106: olfactoriis excitatur, Plin. 30, 11, 29, § 97: in lethargum vergere, id. 32, 10, 38, § 116.
        1. (β) Plur.: ocimum facit lethargos, Plin. 20, 12, 48, § 119; 28, 8, 29, § 116.
  2. B. (Sc. homo.) A lethargic person, Cael. Aur. Acut. 2, 9, 37 sqq.