Thuan sits next to 3 phonetic neighbors — Tuan, Swan, and Quan are the closest matches by sound. Most share Thuan's Vietnamese/Chinese-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"smooth, favorable, agreeable"
"invented name with feminine suffix"
"beam of light, torch"
"evenness of mind, inner balance"
"to sing, to shout for joy, to cry out in praise"
"she who remains, the everlasting one"
"peaceful ruler"
"Victorious mind; one who has conquered the mind"
"lovestruck, mad with love, infatuated"
"original American creation (likely influenced by names meaning God ..."
"phonetic variant of Monet (French surname/artist name)"
"narrow mountain valley"
"God is gracious, little wise one"
"lily"
"olive tree, olive tree planter"
"fire-born, light"
"ewe, female sheep"
"honey bee"
Similar sound: These names share phonetic patterns with Thuan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Vietnamese/Chinese origins, giving them the same cultural heritage as Thuan.
Rhythm: Thuan is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.