Assonance
Etymology
From Latin assonāre, "to answer with the same sound, to respond to": ad- ("to") + sonāre ("to sound"), from sonus ("sound"). The idea is of sounds calling and answering one another. It came into English through French to name vowel-echo as distinct from full rhyme or consonant repetition.
noun · /AS-uh-nunss/
The repetition of similar vowel sounds in nearby words, without full rhyme.
What it names
The internal music of "the rain in Spain" or "a stone-cold no-go" — vowels echoing inside a line to bind it together and slow the ear.
Example
The chorus rode on assonance, stretching the long "o" through "slow," "road," and "home."
Related idea
Consonance echoes consonant sounds rather than vowels; assonance is the vowel counterpart, and unlike alliteration it need not fall at the start of a word.