Doldrums \Dol"drums\, n. pl. [Cf. Gael. doltrum grief, vexation?] A part of the ocean near the equator, abounding in calms, squalls, and light, baffling winds, which sometimes prevent all progress for weeks; -- so called by sailors.

To be in the doldrums, to be in a state of listlessness ennui, or tedium.

Source: Webster's Revised Unabridged Dictionary (1913)