The Collaborative International Dictionary of English v.0.48:

Chalazion \Cha*la"zi*on\, n. [NL., fr. Gr. ? dim. of ? hail,
   pimple.] (Med.)
   A small circumscribed tumor of the eyelid caused by retention
   of secretion, and by inflammation of the Melbomian glands.
   [1913 Webster]

WordNet (r) 3.0 (2006):

chalazion
    n 1: a small sebaceous cyst of the eyelid resulting when a
         Meibomian gland is blocked [syn: chalazion, Meibomian
         cyst]