Other forms: tmeses
Tmesis is splitting a word in two and inserting another word between the halves. In George Bernard Shaw's play Pygmalion, the character Eliza Doolittle uses tmesis when she says, "Abso-bloomin-lutely!"
There are examples of tmesis throughout literature, from Shakespeare to contemporary television. When The Simpsons character Ned Flanders says something like "Wel-diddly-elcome," that's an awkward kind of tmesis. And anyone who says, "A whole nother thing" is also using tmesis, sticking the word "whole" right in the middle of "another." In Greek, tmesis means "a cutting."