Lassitude, n.
Etymology: [L. lassitudo, fr. lassus faint, weary; akin to E. late: cf. F. lassitude. See Late.]
A condition of the body, or mind, when its voluntary functions are performed with difficulty, and only by a strong exertion of the will; languor; debility; weariness. The corporeal instruments of action being strained to a high pitch . . . will soon feel a lassitude. Barrow.
Shades of meaning
Fernald lists lassitude only as an antonym, under entertainment.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given