Brennan sits next to 3 phonetic neighbors — Brianna, Brenna, and Brendan are the closest matches by sound. Most share Brennan's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"descendant of the little drop"
"bird"
"rose (influenced by the flower)"
"bold, fierce settlement"
"James spelled backwards; heard by God"
"descendant of Corraidhín (little spear)"
"moonlight"
"ruler through strength"
"princess, flower"
"diverse, of mixed character"
"divine sky beauty"
"azalea flower (dry earth plant)"
"reborn, born again"
"gracious, beautiful"
"elm grove, place of elms"
"western pool or stream"
"dark challenger"
"white wave"
"bright, shining light"
"western meadow, west field"
Similar sound: These names share phonetic patterns with Brennan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Irish origins, giving them the same cultural heritage as Brennan.
Rhythm: Brennan is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.