The Collaborative International Dictionary of English v.0.48:

doldrums \dol"drums\ (d[o^]l"dr[u^]mz), 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.
   [1913 Webster]

   To be in the doldrums, to be in a state of listlessness
      ennui, or tedium.
      [1913 Webster]

WordNet (r) 3.0 (2006):

doldrums
    n 1: a state of inactivity (in business or art etc); "economic
         growth of less than 1% per year is considered to be
         economic stagnation" [syn: stagnation, stagnancy,
         doldrums]
    2: a belt of calms and light winds between the northern and
       southern trade winds of the Atlantic and Pacific