The Collaborative International Dictionary of English v.0.48:

Siliqua \Sil"i*qua\, n.; pl. Siliquae. [L. See Silique.]
   1. (Bot.) Same as Silique.
      [1913 Webster]

   2. A weight of four grains; a carat; -- a term used by
      jewelers, and refiners of gold.
      [1913 Webster]

WordNet (r) 3.0 (2006):

siliqua
    n 1: narrow elongated seed capsule peculiar to the family
         Cruciferae [syn: silique, siliqua]