The Collaborative International Dictionary of English v.0.48:

Elater \El"a*ter\, n. (Chem.)
   The active principle of elaterium, being found in the juice
   of the wild or squirting cucumber (Ecballium agreste,
   formerly Motordica Elaterium) and other related species. It
   is extracted as a bitter, white, crystalline substance, which
   is a violent purgative.
   [1913 Webster]