The Collaborative International Dictionary of English v.0.48:

Ascidium \As*cid"i*um\ ([a^]s*s[i^]d"[i^]*[u^]m), n.; pl.
   Ascidia (-[.a]). [NL., fr. ascus. See Ascus.]
   1. (Bot.) A pitcher-shaped, or flask-shaped, organ or
      appendage of a plant, as the leaves of the pitcher plant,
      or the little bladderlike traps of the bladderwort
      (Utricularia).
      [1913 Webster]

   2. pl. (Zool.) A genus of simple ascidians, which formerly
      included most of the known species. It is sometimes used
      as a name for the Ascidioidea, or for all the Tunicata.
      [1913 Webster]