WordNet (r) 3.0 (2006):

affixation
    n 1: the result of adding an affix to a root word
    2: formation of a word by means of an affix
    3: the act of attaching or affixing something [syn:
       attachment, affixation]

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "affixation":
   IC analysis, accession, accidence, addition, adhesive, adjunct,
   adjunction, affix, agglutination, allomorph, annexation,
   attachment, augmentation, binding, bond, bound morpheme, clasping,
   conjugation, cutting, declension, derivation, difference of form,
   enclitic, fastener, fastening, formative, free form, girding,
   hooking, immediate constituent analysis, increase, infix,
   infixation, inflection, joining, junction, juxtaposition, knot,
   lashing, ligation, morph, morpheme, morphemic analysis, morphemics,
   morphology, morphophonemics, paradigm, prefix, prefixation,
   proclitic, radical, reinforcement, root, splice, stem, sticking,
   suffix, suffixation, superaddition, superfetation, superjunction,
   superposition, supplementation, theme, tieing, uniting,
   word-formation, zipping