Diminution is the spacing of repeated consonant sounds with the first consonant sound separated by a vowel.

More about Diminution  

Diminution stems from the Latin diminutionem (nominative diminutio), which means “to lessen, diminish.” Musically, diminution is the opposite of augmentation in that there is a proportional diminishing of note-values that were previously used in a melody or motif. This is a technique discussed in Western music and music theory as the embellishment of a long note being divided into shorter values. As a literary device discussed in Kenneth Burke’s essay “On Musicality in Verse: As Illustrated by Some Lines of Coleridge,” diminution in poetry is the inverse of repeated consonant sounds, where the repeated order of sounds separated by vowels is shortened.

Examples of Diminution in Poetry

For instance, in the first tercet of “Morning Song” by Sylvia Plath, the first line contains two examples of diminution. The first is a consonant sound pattern related to the “t” sound: v – –t to f–t. The distance to reaching the “t” sound diminishes from “love set” to “fat.” The second example in this line is the distance of the “g” sound to the “l,” wherein g – – l is diminished to g–l:

           Love set you going like a fat gold watch.
           The midwife slapped your footsoles, and your bald cry
           Took its place among the elements.

Another example is the nineteenth stanza of Part V of “The Rime of the Ancient Mariner” by Samuel Taylor Coleridge:

            Till noon we silently sailed on,
            Yet never a breeze did breathe:
            Slowly and smoothly went the ship,
            Moved onward from beneath.

The “s” and “ly” are repeated first in “silently” and diminished or collapsed in “slowly” and “smoothly.” With this example and Plath’s “Morning Song,” diminution is based on the distance of consonant sounds, with vowels repeated in a diminished distance of the same sounds. The number can vary and can be within a line of the poem or be found in multiple lines of a stanza.