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"
"faith, pledge"
"near the holly trees"
"modern invented name"
"resolute protector"
"a Breton, person from Brittany"
"one strength"
"always, at all times"
"stammering, lisping"
"open grassy land"
"primordial deity, elder god"
"army ruler, power of the army"
"physician, healer"
"ancient, enduring"
"deep valley dwellers"
"narrow water"
"bright settlement, day town"
"truly brave"
"meditation, absorption"
"young warrior, free man"
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.