'Sleepiness' definitions:

Definition of 'sleepiness'

From: WordNet
noun
A very sleepy state; "sleepiness causes many driving accidents" [syn: sleepiness, drowsiness, somnolence] [ant: sleeplessness, wakefulness]

Definition of 'Sleepiness'

From: GCIDE
  • Sleepiness \Sleep"i*ness\, n. The quality or state of being sleepy. [1913 Webster]