Cullen sits next to 5 phonetic neighbors — Colin, Calvin, and Cullan are the closest matches by sound. Most share Cullen's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"at the holly trees"
"strong, virtuous, honorable"
"farmer, earth-worker"
"yellow-haired, blonde"
"yellow, golden"
"strong, upright"
"ruler of the army (Scandinavian form)"
"dweller by the holly"
"roof maker"
"Yahweh sees"
"resolute protector"
"bright fame"
"bright settlement, day town"
"wolf counsel"
"dark settlement (place name)"
"leek farm village"
"descendant of Braonán, tearful one"
"farm steward, granary manager"
"counsel, power"
"voice of God"
"joy, laughter"
Similar sound: These names share phonetic patterns with Cullen — 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 Cullen.
Rhythm: Cullen is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.