Niall sits next to 4 phonetic neighbors — Neil, Neal, and Nils are the closest matches by sound. Most share Niall's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"champion"
"crooked nose; bent river"
"chain link, connection"
"brave as a wild boar"
"peaceful ruler"
"people of gentle birth"
"flowing down (from Jordan)"
"stubborn one"
"payment, redemption (word association)"
"spring, fertility (earlier meaning)"
"pledge, oath"
"red-haired, little redhead"
"wooded land"
"God is gracious"
"shelter, protection"
"God has remembered"
"world ruler"
"bear"
"little fire"
"from the town, settlement"
Similar sound: These names share phonetic patterns with Niall — 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 Niall.
Rhythm: Niall is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.