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"
"crooked nose"
"old, long past"
"bright settlement, day town"
"free man"
"song, singing bird"
"little raven"
"narrow water"
"poet, bard"
"gentle breeze"
"ruler of all, universal ruler"
"the koa (warrior tree)"
"thatcher, roof builder"
"watchful, vigilant (via Casey)"
"the promised land"
"brave in battle, vigilant"
"son of Harry, home ruler"
"honorable, morally excellent"
"wise, judicious"
"dragon, serpent"
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.