The Collaborative International Dictionary of English v.0.48:

Suppository \Sup*pos"i*to*ry\, n.; pl. Suppositories. [LL.
   suppositorium, fr. L. suppositorius that is placed
   underneath: cf. F. suppositoire. See Supposition.] (Med.)
   A pill or bolus for introduction into the rectum; esp., a
   cylinder or cone of medicated cacao butter.
   [1913 Webster]

WordNet (r) 3.0 (2006):

suppository
    n 1: a small plug of medication designed for insertion into the
         rectum or vagina where it melts