Brett sits next to 4 phonetic neighbors — Bret, Brad, and Trent are the closest matches by sound. Most share Brett's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"a Breton, person from Brittany"
"river (from Celtic afon)"
"stream, small brook"
"eternal, perpetual"
"narrow strait"
"from the city of lions"
"agreement to stop fighting, temporary peace"
"beginning, origin"
"spear ruler (from Gerald)"
"strong, upright"
"treasure, to store (possible Arabic root)"
"tournament fighter"
"the island, island dweller"
"noble eagle (adal + aro)"
"cheerful, optimistic"
"earnestness, sincerity"
"God is good"
"Kryptonian birth name of Superman"
"bright, splendid"
"dark warrior"
Similar sound: These names share phonetic patterns with Brett — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Celtic/Old French origins, giving them the same cultural heritage as Brett.
Rhythm: Brett is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.