Definition of "capitulum"

(botany) A densely clustered inflorescence composed of a large number of individual florets arising from a platform-like base.  examples

(arachnology) The head-like mouthpart apparatus of a tick, including the palpi, mandibles, and hypostome.

(anatomy) A small protuberance on a bone which articulates into another bone to form a ball-and-socket joint.  examples

(entomology, obsolete) The enlarged end of a proboscis.