Hypnagogic \hip-nuh-GOJ-ik\ or \hip-nuh-GOH-jik\ , adjective;
1. Of, pertaining to, or occurring in the state of drowsiness preceding sleep.
This word dates to 1886 from French hypnagogique which derives from Greek hypnos + agogos ("sleep" + "leading"). Hypnos ultimately derives from the Proto-Indo-European base *swep- meaning "sleep". Agogos comes from the Proto-Indo-European root *ag- ("to drive"), which is also the forebear of English act.
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Thursday, February 24
Etymologies come from the Oxford English Dictionary and/or Etymonline.com