Regan sits next to 4 phonetic neighbors — Reagan, Keegan, and Brogan are the closest matches by sound. Most share Regan's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"little king, of royal descent"
"warlike, martial"
"thunder"
"rye meadow"
"from the River Clyde"
"of the night"
"rose field, field of roses"
"cart driver, cart maker"
"little king"
"roses"
"homestead on the rock"
"flourishing, like a flower"
"varies by given names the initials represent"
"white man, fair-haired man"
"hospitable"
"heart, mind"
"wealthy protector, guardian of prosperity"
"gift of God (by association with Zay names)"
"the free one, freedom"
"the kamani tree (Calophyllum inophyllum)"
"realm, dominion"
Similar sound: These names share phonetic patterns with Regan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Irish Gaelic origins, giving them the same cultural heritage as Regan.
Rhythm: Regan is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.