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