Gareth sits next to 3 phonetic neighbors — Garrett, Garth, and Garreth are the closest matches by sound. Most share Gareth's Welsh cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"gentle, gentleness"
"star"
"noble born"
"willow farm, ledge estate"
"horseman, cavalryman"
"priceless, beyond praise"
"Geirrapos island, grassy island"
"defender (Greek mythological meaning)"
"homestead by the stream"
"of Mars, warlike"
"of divine origin"
"dark complexion"
"son of the grey-haired one"
"lake meadow"
"heri (army) + beraht (bright)"
"wolf-like, fierce hunter"
"song, joy"
"lord of the sea"
"son of Rhys, ardor and enthusiasm"
"charcoal merchant, coal worker"
"one who resembles God"
Similar sound: These names share phonetic patterns with Gareth — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Welsh origins, giving them the same cultural heritage as Gareth.
Rhythm: Gareth is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.