Trochaic substitution

A trochaic substitution occurs when a trochee replaces an iamb in a verse of poetry that employs iambic pentameter as its meter. Specifically, a two-syllable foot comprising a slacked syllable followed by a stressed syllable (- /) is replaced by a two-syllable foot comprising a stressed syllable followed by a slacked syllable (/ -).

A trochaic substitution is often used to emphasize a word for effect, as in the following example from John Donne's Holy Sonnet 14:

"Batter my heart three-personed God, for You / As yet but knock, breathe, shine and seek to mend."