somnolence

from WordNet (r) 3.0 (2006)

somnolence
    n 1: a very sleepy state; "sleepiness causes many driving
         accidents" [syn: {sleepiness}, {drowsiness}, {somnolence}]
         [ant: {sleeplessness}, {wakefulness}]

from The Collaborative International Dictionary of English v.0.48

Somnolence \Som"no*lence\, Somnolency \Som"no*len*cy\, n. [L.
   somnolentia: cf. F. somnolence.]
   Sleepiness; drowsiness; inclination to sleep.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

48 Moby Thesaurus words for "somnolence":
      acedia, apathy, boredom, doziness, drowsiness, dullness,
      enervation, ennui, fatigue, heaviness, hebetude, inanimation,
      indifference, jadedness, lackadaisicalness, languidness,
      languishment, languor, languorousness, lassitude, lenitude, lentor,
      lethargy, lifelessness, listlessness, oscitancy, oscitation,
      pandiculation, passivity, phlegm, satedness, sleepiness, sloth,
      slothfulness, slowness, sluggishness, somnolency, stretching,
      stupefaction, stupor, supineness, torpidity, torpidness, torpitude,
      torpor, weariness, world-weariness, yawning