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"
"son of"
"associated with the church"
"little dark one"
"narrow strait"
"battle, warrior"
"helpful; assistant; descendant of the helpful one"
"God is my judge"
"consecrated, increased"
"victory of the people (from Nicholas)"
"Yahweh is merciful"
"little rock, harmony"
"Frenchman"
"God is gracious"
"fair-haired hero; white warrior"
"red"
"from the city of Troy"
"Yahweh is merciful"
"son of Egan, little fire"
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.