Lethargy, n.; pl. -gies.
Etymology: [F. léthargie, L. letgargia, Gr. Lethe.]
1. Morbid drowsiness; continued or profound sleep, from which a person can scarcely be awaked.
2. A state of inaction or indifference. Europe lay then under a deep lethargy. Atterbury.
1 other Webster entry under this spelling
Lethargy, v. t.
To lethargize. [Obs.] Shak.
Shades of meaning
Fernald has no entry of its own for lethargy; he lists it under apathy, stupor.
Where he writes about it:
The apathy of disease is a mental affection, a state of morbid indifference; lethargy is a morbid tendency to heavy and continued sleep, from which the patient may perhaps be momentarily aroused. — from stupor