Tmesis

[Sarah]

The separation of the parts of a compound word by theintervention of one or more words; as, in what place soever, forwhatsoever place.

[Sarah]

In grammar and rhetoric, the separation of the parts of a
compound word, now generally done for humorous effect

[Sarah]

The art of breaking one word into two parts, inserting a different word (often an expletive) in between those two parts, hence forth turning two different words into one in order to give extra emphasis

from Greek, a cutting, from temnein, to cut (see tem- in Indo-European roots)