The Collaborative International Dictionary of English v.0.48:

Suffix \Suf*fix"\, v. t. [imp. & p. p. Suffixed; p. pr. & vb.
   n. Suffixing.]
   To add or annex to the end, as a letter or syllable to a
   word; to append.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Suffix \Suf"fix\, n. [L. suffixus, p. p. of suffigere to fasten
   on, to affix; sub under + figere to fix: cf. F. suffixe. See
   Fix.]
   1. A letter, letters, syllable, or syllables added or
      appended to the end of a word or a root to modify the
      meaning; a postfix.
      [1913 Webster]

   2. (Math.) A subscript mark, number, or letter. See
      Subscript, a.
      [1913 Webster]

WordNet (r) 3.0 (2006):

suffix
    n 1: an affix that is added at the end of the word [syn:
         suffix, postfix]
    v 1: attach a suffix to; "suffix words" [ant: prefix]