Merlin sits next to 4 phonetic neighbors — Marlin, Myrddin, and Erlin are the closest matches by sound. Most share Merlin's Welsh cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"sea fortress"
"nobleman, warrior"
"oak meadow, clearing in the oaks"
"son of Carr, from the marsh"
"held by the heel"
"son of Gerald"
"friend of Yahweh"
"God has remembered"
"from the kaupa (trading) land"
"inspired counsel"
"bridge homestead"
"rival, eager to emulate"
"capable with a spear"
"love"
"steep valley settlement"
"from the surname of poet W.H. Auden"
"majestic, venerable"
"little hawk"
"settlement by the sea"
"settlement by a bird-trap"
"enlightenment, awakening"
Similar sound: These names share phonetic patterns with Merlin — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Brittonic/Welsh origins, giving them the same cultural heritage as Merlin.
Rhythm: Merlin is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.