n. The insertion of one or more words between the components of a compound word.
the GNU version of the Collaborative International Dictionary of English
n. The separation of the parts of a compound word by the intervention of one or more words.
The Century Dictionary and Cyclopedia
n. In grammar, a figure by which a compound word is separated into two parts, and one or more words are inserted between them: as, “of whom be thou ware also” (2 Tim. iv. 15), for “of whom beware thou also.” Also called diacope.
Word Usage
"This is called tmesis: "What man soever" we've put one word between the syllables of another word."