Niamh sits next to 3 phonetic neighbors — Neve, Nieve, and Eve are the closest matches by sound. Most share Niamh's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"bright, radiant, lustrous"
"superior, one who rules"
"from Derby"
"fairy palace, admirable"
"slender, beautiful"
"from Lorn, from the district of Argyll, Scotland"
"little dark one"
"radiance, brilliance, splendor"
"youthful"
"river, stream"
"kingly, noble"
"strength, power"
"lamb"
"powerful in battle"
"gift of God's grace"
"pure"
"sea warrior"
Similar sound: These names share phonetic patterns with Niamh — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Old Irish origins, giving them the same cultural heritage as Niamh.
Rhythm: Niamh is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.