The Collaborative International Dictionary of English v.0.48:

Elaterium \El`a*te"ri*um\, n. [L., fr. Gr. ?, neut. of ?
   driving. See 2d Elater.]
   A cathartic substance obtained, in the form of yellowish or
   greenish cakes, as the dried residue of the juice of the wild
   or squirting cucumber (Ecballium agreste, formerly called
   Momordica Elaterium).
   [1913 Webster]

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]