Ciel sits next to 5 phonetic neighbors — Siel, Cecil, and Celine are the closest matches by sound. Most share Ciel's French-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"sky, heaven"
"that which has not yet come"
"lord, ruler"
"hall stone, from the rocky hall"
"ewe plus waterfall"
"fairy queen; princess"
"pure, chaste"
"crooked nose"
"gentle wind"
"world, universe"
"maiden, heart"
"radiant, brilliant light"
"variant of Kayla, meaning 'keeper of the keys' or 'pure'"
"of the Cree people"
"song, poem"
"the act of choosing, selected one"
"olive tree"
"from Wales, land of the Welsh"
"bright, clear, famous"
"variant of Dora, gift"
"bear strength"
Similar sound: These names share phonetic patterns with Ciel — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have French origins, giving them the same cultural heritage as Ciel.
Rhythm: Ciel is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.