Synonyms for Lethargic:

adj.

dense (adjective)
impassive.
dull (adjective)
dull, sleepy, thick-witted, blunt, dim, ponderous, sluggish, obtuse, dense, loutish, cloddish, soporific, doltish, stupefied, slow, apathetic, besotted, drowsy, comatose, bovine, boorish, benumbed.
fatigued (adjective)
Flagged, Wayworn, weary, tired, Frazzled, enervated, drowsy, sleepy, worn-out, exhausted, run down, sluggish, fatigued.
inactive (adjective)
unemployed, unmoving, motionless, stationary, idle, dormant, inactive, sleepy, jobless, sedentary, Snail-paced, lifeless, still, unworking.
inert (adjective)
listless, sluggish, sedentary, still, static, stagnant, stationary, inanimate, apathetic, immobile, dormant, passive, inactive, paralytic, insensible, languorous, Reposing, indifferent, inert, catatonic, idle, lifeless, comatose, motionless, languid, vegetative.
lazy, sluggish (adjective)
inert, comatose, apathetic, stolid, dopey, impassive, lackadaisical, indifferent, phlegmatic, torpid, drowsy, passive, sleepy, inactive, slow, idle, stupefied, listless, enervated, languorous, dull, slothful, languid, dormant.
lethargic (adjective)
tired, drooping, dopey, listless, drugged, lumpish, torpid, slothful, insensible, sluggish, lackadaisical, dull, languid, phlegmatic, lifeless, leisurely, slow, benumbed, leaden, apathetic, lazy, languorous, unhurried, indolent.
slow (adjective)
poky, dawdling, Loitering, creeping, dragging, Trudging, sluggish, leisurely, Delaying, plodding, slow, phlegmatic, slowpoke, crawling, lingering.

n.

hebetudinous, action. unconcerned, detached, indifferent, feelings, uninterested, unresponsive, stolid, impassive, incurious. lethargic (noun)
unergetic, logy, languorous, lackadaisical, listless, stuporous, dazed, dreamy, groggy, foggy, languid.
tired (noun)
dozy, on your last legs, all in.

Other synonyms:

hebetudinous. uninterested, unresponsive, impassive, stolid, unconcerned. incurious. indifferent, detached. Other relevant words:
impassive, indifferent, dozy, detached, uninterested, all in, dazed, foggy, dreamy, incurious, stuporous, stolid, groggy, action, unconcerned, unresponsive, feelings, hebetudinous, unergetic, logy.

Usage examples for lethargic

  1. His voice roused her from the sort of lethargic state into which she had dropped for a moment. – Sara, a Princess by Fannie E. Newberry
  2. No one I think can doubt that much good was effected by the first preaching of Wesley and his disciples, for at that time our church was in a lethargic state, and the lower orders shamefully neglected in spiritual matters in many parts of England. – Christian Sects in the Nineteenth Century by Caroline Frances Cornwallis
  3. She was so blissfully lethargic and she was not thinking at all of money or cotton. – The Desert Fiddler by William H. Hamby