Brilliant sits next to 3 phonetic neighbors — Brylinn, Beryllian, and Brilliance are the closest matches by sound. Most share Brilliant's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"shining, sparkling, full of light"
"good person, calm"
"opening, unfolding"
"keeper of records, secretary"
"invented name combining La- (the) with -viah (echoing Hebrew -iah, ..."
"Pledged to God; my God is an oath"
"kiss"
"dear friend, beloved companion"
"Her Majesty — a royal title indicating supreme authority and dignity"
"important, significant one"
"snow"
"divine authority over creation"
"moonlight, shining light"
"pure"
"foxglove flower"
"messenger of the gods, boundary marker"
"lake, waterfall (from Welsh -lynn component)"
Similar sound: These names share phonetic patterns with Brilliant — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have French via Italian origins, giving them the same cultural heritage as Brilliant.
Rhythm: Brilliant is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.