Castle sits next to 4 phonetic neighbors — Castel, Castiel, and Pascal are the closest matches by sound. Most share Castle's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"fortified stronghold"
"royal, kingly"
"resolute protector"
"ascending, going upward"
"from the island of Cyprus"
"edge, border of land"
"solid, strong foundation"
"Trey's town, three's farm"
"the metal copper"
"manly beauty, sun god"
"warrior, champion fighter"
"city of Athena; city of wisdom"
"supplanter, one who grabs the heel"
"fire of God"
"song sung to a harp"
"strengthened by God"
"one who rules"
"new house, bright place"
"from the lake"
"ruler of the home"
"battle, fighter, combatant"
Similar sound: These names share phonetic patterns with Castle — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin/Norman French origins, giving them the same cultural heritage as Castle.
Rhythm: Castle is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.