Sound & Diction
Tmesis
Inserting a word into another word or fixed phrase: “abso-bloody-lutely.” The interruption emphasizes the inserted expression.
"un-bloody-believable"
Don't confuse it with Parenthesis. Infixation is the linguist's term for the same surgery; parenthesis interrupts a sentence, tmesis interrupts a single word.
Examples
That was abso-bloody-lutely impossible.
“Bloody” is inserted inside the word “absolutely.”
The rest of the family
Alliteration Assonance Onomatopoeia Neologism Archaism Solecism Epithet