Sound & Diction
Assonance
Repeating vowel sounds in nearby words, as in “the deep green sea.” The repeated sounds can link words or establish a pattern within a line.
“Deep green sea”: the stressed vowels repeat /iː/.
Don't confuse it with Alliteration. Alliteration repeats initial consonants; consonance repeats consonants anywhere; assonance is vowels only.
Examples
The deep green sea.
“Deep,” “green,” and “sea” repeat the /iː/ vowel sound.
Slow boats float home.
The stressed vowel in the nearby words repeats /oʊ/ in common American pronunciation.
The rest of the family
Alliteration Onomatopoeia Tmesis Neologism Archaism Solecism Epithet