Source : Webster's Revised Unabridged Dictionary (1913)

Lethargic \Le*thar"gic\ (l[-e]*th[aum]r"j[i^]k), Lethargical
\Le*thar"gic*al\ (-j[i^]*kal), a. [L. lethargicus, Gr.
   lhqargiko`s: cf. F. l['e]thargique. See {Lethargy}.]
   Pertaining to, affected with, or resembling, lethargy;
   morbidly drowsy; dull; heavy. -- {Le*thar"gic*al*ly}, adv. --
   {Le*thar"gic*al*ness}, n. -- {Le*thar"gic*ness}, n.

Source : WordNet®

lethargic
     adj : deficient in alertness or activity; "bullfrogs became
           lethargic with the first cold nights" [syn: {unergetic}]
           [ant: {energetic}]