The Collaborative International Dictionary of English v.0.48:

Cupule \Cu"pule\ (k?"p?l), n. [See Cupola.]
   1. (Bot.) A cuplet or little cup, as of the acorn; the husk
      or bur of the filbert, chestnut, etc.
      [1913 Webster]

   2. (Zool.) A sucker or acetabulum.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cupule
    n 1: cup-shaped structure of hardened bracts at the base of an
         acorn [syn: cupule, acorn cup]
    2: a sucker on the feet of certain flies