Sullivan sits next to 4 phonetic neighbors — Callum, Sullivan, and Donovan are the closest matches by sound. Most share Sullivan's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"descendant of the dark one"
"red-haired, ruddy complexion"
"lives near reeds"
"from the hay enclosure"
"chosen savior"
"greatest, largest"
"red king, famous ruler"
"patrician, of noble birth"
"from the castle, place near the ditch"
"surname origin from Gaelic Mac Caid"
"son of Jove, divine descent"
"battle worthy"
"first, chief"
"precious and brave"
"little fire"
"firm foundation"
"from Antwerp"
"invented name, possibly evoking sky"
"of the gens Lucia (light)"
"good man"
"free man"
Similar sound: These names share phonetic patterns with Sullivan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Irish Gaelic origins, giving them the same cultural heritage as Sullivan.
Rhythm: Sullivan is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.