infix

from The American Heritage® Dictionary of the English Language, 5th Edition.

• transitive verb To fix in the mind; instill.
• transitive verb Linguistics To insert (a morphological element) into the body of a word.
• noun An inflectional or derivational element appearing in the body of a word. For example, in Tagalog, the active verb sulat, “write,” can be converted to a passive, “written,” by inserting the infix –in–, yielding sinulat.

from The Century Dictionary.

• noun Something infixed; in grammar, an element having the value of a suffix or a prefix, but inserted in the body of a word, as practised in some languages.
• To fix or fasten in; insert forcibly; implant firmly: as. to infix a dart; to infix facts in the memory.
• To insert additionally or accessorily. See infix, n.

from the GNU version of the Collaborative International Dictionary of English.

• noun rare Something infixed.
• noun (Grammar) An element that is inserted into the body of an elemt which it threby modifies, as a letter within a word.
• transitive verb To set; to fasten or fix by piercing or thrusting in.
• transitive verb To implant or fix; to instill; to inculcate, as principles, thoughts, or instructions.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb transitive To instill.
• verb transitive, linguistics To insert a morpheme inside an existing word.
• noun linguistics A morpheme inserted inside an existing word, such as -i- and -o- in English. This adds additional meaning or alters the meaning of the morpheme it is inserted into.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an affix that is inserted inside the word
• verb put or introduce into something
• verb attach a morpheme into a stem word