Arthur sits next to 3 phonetic neighbors — Archer, Arturo, and Artur are the closest matches by sound. Most share Arthur's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"bear, bear-like strength"
"young warrior"
"full of goodness"
"God will add, God will increase"
"defender of men"
"spotted stone"
"soldier"
"bright fame"
"God is gracious (via Jack, from John)"
"strong, mighty"
"citizen of Rome, Roman"
"God has healed"
"winding valley"
"handsome at birth"
"venerable"
"whole-hearted, faithful"
"Christian (the religion)"
"lion (leonem)"
"greatest"
"king's town"
"from the brook"
Similar sound: These names share phonetic patterns with Arthur — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Brythonic Celtic origins, giving them the same cultural heritage as Arthur.
Rhythm: Arthur is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.