Delain sits next to 4 phonetic neighbors — Elaine, Delaine, and Delane are the closest matches by sound. Most share Delain's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"of the alder tree"
"Joining; concord; agreement - from Greek harmonia, the goddess of h..."
"fairy"
"messenger of God; angel"
"faith"
"nickname, playful diminutive"
"Possibly a variant of Teresa/Therese, meaning to reap or harvest"
"moon goddess, famous warrior"
"devoted to Demeter, goddess of the harvest; earth lover"
"Of the sea, warrior; defender of the sea"
"Gaelic form of Jane/Jean"
"prince, hill settlement"
"supplanter"
"pure"
"Variant of Sherman; from the shearing settlement"
"free person, strong one (via Carla/Carl)"
Similar sound: These names share phonetic patterns with Delain — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have French de l'aulne origins, giving them the same cultural heritage as Delain.
Rhythm: Delain is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.