The Collaborative International Dictionary of English v.0.48:

Croton \Cro"ton\ (kr?"t?n), n. [Gr. ????, prop., a tick, which
   the seed of the croton resembles.] (Bot.)
   A genus of euphorbiaceous plants belonging to tropical
   countries.
   [1913 Webster]

   Croton oil (Med.), a viscid, acrid, brownish yellow oil
      obtained from the seeds of Croton Tiglium, a small tree
      of the East Indies. It is a most powerful drastic
      cathartic, and is used externally as a pustulant.
      [1913 Webster]

WordNet (r) 3.0 (2006):

croton oil
    n 1: viscid acrid brownish-yellow oil from the seeds of Croton
         tiglium having a violent cathartic action