Source : Webster's Revised Unabridged Dictionary (1913)

Onagraceous \On`a*gra"ceous\, Onagrarieous \On`a*gra*ri"e*ous\,
   a. [From NL. Onagra an old scientific name of the evening
   primrose (Enothera), fr. Gr. ? a kind of plant; of uncertain
   origin.] (Bot.)
   Pertaining to, or resembling, a natural order of plants
   ({Onagrace[ae]} or {Onagrarie[ae]}), which includes the
   fuchsia, the willow-herb ({Epilobium}), and the evening
   primrose ({[OE]nothera}).

Source : WordNet®

Oenothera
     n : chiefly North American herbs with usually nocturnal flowers
         [syn: {genus Oenothera}]