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]

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "suffix":
   IC analysis, PS, Parthian shot, accidence, add, addendum, addition,
   adjoin, affix, affixation, afterthought, agglutinate, allomorph,
   allonge, amend, annex, append, appendix, attach, back matter,
   bound morpheme, burden, chorus, coda, codicil, colophon,
   commentary, complicate, conclusion, conjoin, conjugation,
   consequence, continuance, continuation, cutting, declension,
   decorate, derivation, desinence, difference of form, double take,
   dying words, enclitic, encumber, ending, envoi, epilogue,
   follow-through, follow-up, formative, free form, glue on, hitch on,
   immediate constituent analysis, infix, infixation, inflection,
   interlineation, interpolation, join, join with, last words,
   marginalia, morph, morpheme, morphemic analysis, morphemics,
   morphology, morphophonemics, note, ornament, paradigm,
   parting shot, paste on, peroration, plus, postface, postfix,
   postlude, postscript, prefix, prefixation, proclitic, put with,
   radical, refrain, rider, root, saddle with, scholia,
   second thought, sequel, sequela, sequelae, sequelant, sequent,
   sequitur, slap on, stem, subjoin, subscript, suffixation, superadd,
   superpose, supplement, swan song, tack on, tag, tag on, tail,
   theme, unite with, word-formation