What is Infix?

Infix definition and meaning on Dictionary terms:
verb (used with object)
to fix, fasten, or drive in: He infixed the fatal spear.
to implant: to infix a habit.
to instill (a fact, idea, etc.) in the mind or memory; impress.
Grammar. to add as an infix.

verb (used without object)
Grammar. (of a linguistic form) to admit an infix.

Grammar. an affix that is inserted within the body of the element to which it is added, as Latin m in accumb?