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"
"dweller near the marsh"
"peace"
"lion"
"son of Carr, from the marsh"
"American creative variant of Trevor"
"uncle"
"high will, desiring much"
"friend of Yahweh"
"dove"
"given by God"
"variant of Alexander (defender of men)"
"wealthy protector"
"of the forest, woodland"
"from the surname of poet W.H. Auden"
"armed host, military force"
"famous warrior"
"clay, mortal man"
"servant, worshipper of God"
"anglicization of Welsh Llwyd"
"handsome, beautiful"
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.