The Collaborative International Dictionary of English v.0.48:

Capitulum \Ca*pit"u*lum\ (k[.a]*p[i^]t"[-u]*l[u^]m), n.; pl.
   Capitula (k[.a]*p[i^]t"[-u]*l[.a]). [L., a small head.]
   1. A thick head of flowers on a very short axis, as a clover
      top, or a dandelion; a composite flower. A capitulum may
      be either globular or flat. --Gray.
      [1913 Webster]

   2. (Anat.) A knoblike protuberance of any part, esp. at the
      end of a bone or cartilage.

   Note: [See Illust. of Artiodactyla.]
         [1913 Webster]

WordNet (r) 3.0 (2006):

capitulum
    n 1: a dense cluster of flowers or foliage; "a head of
         cauliflower"; "a head of lettuce" [syn: capitulum,
         head]
    2: fruiting spike of a cereal plant especially corn [syn: ear,
       spike, capitulum]
    3: an arrangement of leafy branches forming the top or head of a
       tree