The Collaborative International Dictionary of English v.0.48:

ketchup \ketch"up\, n. [Probably of East Indian origin, because
   it was originally a kind of East Indian pickles. Cf. also
   Malay k[e^]chap fish sauce. --MW10.]
   A pureed table sauce made predominantly from tomatoes,
   flavored with onions, sugar, salt and spices; called also
   tomato ketchup. The term is also applied to pureed sauces
   containing mushrooms, walnuts, etc., being called in such
   cases mushroom ketchup, walnut ketchup, etc. [Written
   also catsup and catchup.]
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Catchup \Catch"up\, Catsup \Cat"sup\, n. [Probably of East
   Indian origin, because it was originally a kind of East
   Indian pickles. Cf. also Malay k[e^]chap fish sauce. --MW10.]
   A pureed table sauce made predominantly from tomatoes,
   flavored with onions, sugar, salt and spices; called also
   tomato ketchup. The term is also applied to pureed sauces
   containing mushrooms, walnuts, etc., being called in such
   cases mushroom ketchup, walnut ketchup, etc. [Written
   also ketchup.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

ketchup
    n 1: thick spicy sauce made from tomatoes [syn: catsup,
         ketchup, cetchup, tomato ketchup]