The Collaborative International Dictionary of English v.0.48:

Contributor \Con*trib"u*tor\, n.
   One who, or that which, contributes; specifically, one who
   writes articles for a newspaper, magazine, or book.
   [1913 Webster]

WordNet (r) 3.0 (2006):

contributor
    n 1: someone who contributes (or promises to contribute) a sum
         of money [syn: subscriber, contributor]
    2: a writer whose work is published in a newspaper or magazine
       or as part of a book