verb

• (transitive, archaic) To set; to fasten or fix by piercing or thrusting in.
  "to infix a sting, spear, or dart"
• (transitive) To instill.
• (transitive, linguistics) To insert a morpheme inside an existing word.

noun

• (some authors when describing agglutinative languages, otherwise dated) A prefix that is not at the beginning of a word, such as the con- of reconcile, or a suffix that is not at the end of a word, such as the -al of nationality.
  "The infix position contains (pronominal) object markers, showing agreement with the object(s), which might be one or more noun phrases following the verb, or a foregoing or previously mentioned object marking."
• (Bantu linguistics, dated) A prefix that always occurs in the position immediately before the verb root, and which may in turn be preceded by other prefixes.
• (proscribed) Synonym of interfix.