Assonance

Assonance is "the repetition of identical or similar phonemes in words or syllables that occur close together," and in American usage the word is reserved for vowel sounds. "Assonance occurs more often in verse than in prose," "vocalic assonance is an important element in verse," and rhyme is "a special case of assonance," its word endings identical, as in fog and log.

For the prose writer assonance is mood without meaning: a chain of long vowels slows and darkens a sentence, a run of brighter ones lifts it, and because the echo works under the ear it colors a passage without announcing itself the way alliteration does. Watch it when a sentence begins to sound better than it thinks; that drift is one seed of purple prose.