Rex sits next to 3 phonetic neighbors — Max, Tex, and Dex are the closest matches by sound. Most share Rex's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"king"
"shelter, shield"
"noble eagle (adal + aro)"
"vigor and power"
"lasting impact, heritage"
"the ram"
"new"
"modern American creation"
"son of Walter"
"dark settlement"
"stony meadow"
"Yahweh has created"
"lover of horses"
"resolute protector's son"
"son of Jeffrey, son of God's peace"
"son of the wealthy guardian"
"from the River Clyde"
"remedy, cure (folk etymology)"
"of, from (Dutch)"
"healer (via Jason/Iason)"
"God is gracious"
Similar sound: These names share phonetic patterns with Rex — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin origins, giving them the same cultural heritage as Rex.
Rhythm: Rex is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.