The Collaborative International Dictionary of English v.0.48:

Cheddar \Ched"dar\, a.
   Of or pertaining to, or made at, Cheddar, in England; as,
   Cheddar cheese.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Cheddar
    n 1: a village in southwestern England where cheddar cheese was
         first made
    2: hard smooth-textured cheese; originally made in Cheddar in
       southwestern England [syn: cheddar, cheddar cheese,
       Armerican cheddar, American cheese]