The Collaborative International Dictionary of English v.0.48:

Sty \Sty\, n. [For older styan, styanye, understood as sty on
   eye, AS. st[imac]gend (sc. e['a]ge eye), properly, rising, or
   swelling (eye), p. p. of st[imac]gan to rise. See Sty, v.
   i.] (Med.)
   An inflamed swelling or boil on the edge of the eyelid.
   [Written also stye.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Stye \Stye\, n.
   See Sty, a boil.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stye
    n 1: an infection of the sebaceous gland of the eyelid [syn:
         sty, stye, hordeolum, eye infection]