Source : Webster's Revised Unabridged Dictionary (1913)

Agrypnotic \Ag`ryp*not"ic\, n. [Gr. ? sleepless; ? to chase,
   search for + ? sleep: cf. F. agrypnotique.]
   Anything which prevents sleep, or produces wakefulness, as
   strong tea or coffee.

Source : WordNet®

agrypnotic
     adj : of or pertaining to agrypnia