The Collaborative International Dictionary of English v.0.48:

carcinoid \carcinoid\ [From Gr. karki`nos, a crab + -oid.] n.
   A small tumor (benign or malignant) arising from the mucosa
   of the gastrointestinal tract; it is usually associated with
   excessive secretion of serotonin.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

carcinoid
    n 1: a small tumor (benign or malignant) arising from the mucosa
         of the gastrointestinal tract; usually associated with
         excessive secretion of serotonin