The Collaborative International Dictionary of English v.0.48:
drowsiness \drow"si*ness\, n. State of being drowsy. --Milton. [1913 Webster]WordNet (r) 3.0 (2006):
drowsiness n 1: a very sleepy state; "sleepiness causes many driving accidents" [syn: sleepiness, drowsiness, somnolence] [ant: sleeplessness, wakefulness]