The Collaborative International Dictionary of English v.0.48:

Infix \In*fix"\, v. t. [imp. & p. p. Infixed; p. pr. & vb. n.
   Infixing.] [L. infixus, p. p of infigere to infix; pref.
   in- in + figere to fix: cf. F. infixer. See Fix.]
   1. To set; to fasten or fix by piercing or thrusting in; as,
      to infix a sting, spear, or dart. --Shak.
      [1913 Webster]

            The fatal dart a ready passage found,
            And deep within her heart infixed the wound.
                                                  --Dryden.
      [1913 Webster]

   2. To implant or fix; to instill; to inculcate, as
      principles, thoughts, or instructions; as, to infix good
      principles in the mind, or ideas in the memory.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Infix \In"fix\, n.
   1. Something infixed. [R.] --Welsford.
      [1913 Webster]

   2. (Grammar) An element that is inserted into the body of an
      elemt which it threby modifies, as a letter within a word.
      [PJC]

WordNet (r) 3.0 (2006):

infix
    n 1: an affix that is inserted inside the word
    v 1: put or introduce into something; "insert a picture into the
         text" [syn: insert, infix, enter, introduce]
    2: attach a morpheme into a stem word

Moby Thesaurus II by Grady Ward, 1.0:

140 Moby Thesaurus words for "infix":
   IC analysis, accidence, add, adjoin, affix, affixation,
   agglutinate, allomorph, allonge, annex, append, appendix, aside,
   attach, beat into, bed, bound morpheme, brainwash, burden,
   catechize, coda, codicil, commentary, complicate, condition,
   confirm, conjoin, conjugation, cutting, declension, decorate,
   deep-dye, define, derivation, difference of form, embed, enclitic,
   encumber, engraft, engrave, entrench, envoi, epilogue, episode,
   establish, etch, fit in, fix, formative, found, free form, glue on,
   grave, ground, hitch on, imbue, immediate constituent analysis,
   impact, implant, impregnate, impress, imprint, inculcate,
   indoctrinate, infixation, inflection, infuse, ingrain, injection,
   inlay, inoculate, inscribe, inseminate, insert, insertion,
   insinuation, instill, intercalation, interjection, interlineation,
   interlocution, interpolation, introduction, jam, join with, lodge,
   marginalia, morph, morpheme, morphemic analysis, morphemics,
   morphology, morphophonemics, note, obiter dictum, ornament, pack,
   paradigm, parenthesis, paste on, plant, plus, postfix, postscript,
   prefix, prefixation, print, proclitic, program, put with, radical,
   remark, rider, root, saddle with, scholia, seat, set, set in,
   settle, side remark, slap on, stamp, stem, stereotype, subjoin,
   suffix, suffixation, superadd, superpose, tack on, tag, tag on,
   tail, tessellate, theme, tossing-in, unite with, wedge,
   word-formation