Cillian sits next to 4 phonetic neighbors — Killian, Kellan, and Killean are the closest matches by sound. Most share Cillian's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"strife, war"
"may God protect"
"little dark one"
"associated with the church"
"brave in battle"
"son of Egan, little fire"
"dark warrior"
"sea-born, born of the sea"
"handsome, cheerful"
"son of the fair one"
"man, the light"
"noble, illustrious"
"helpful; assistant; descendant of the helpful one"
"descendant of the dark one"
"handsome; fair one"
"from the city of Troy"
"noble, high"
"God is gracious"
Similar sound: These names share phonetic patterns with Cillian — 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 Cillian.
Rhythm: Cillian is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.