The Collaborative International Dictionary of English v.0.48:

Pronoun \Pro"noun\, n. [Pref. pro- + noun: cf. F. pronom, L.
   pronomen. See Noun.] (Gram.)
   A word used instead of a noun or name, to avoid the
   repetition of it. The personal pronouns in English are I,
   thou or you, he, she, it, we, ye, and they.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pronoun
    n 1: a function word that is used in place of a noun or noun
         phrase