Rio sits next to 4 phonetic neighbors — Leo, Mio, and Cleo are the closest matches by sound. Most share Rio's Spanish-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"river"
"I see the sun, sun goddess"
"cheerful, joyful"
"yew wood, archer"
"star sun"
"belonging to Julius"
"sequence of musical notes"
"sky blue, azure color"
"ice rule, pledged"
"blue"
"steadfast, constant, unwavering"
"other, foreign"
"follower of Christ"
"my God is Yahweh"
"one with spunk and spirit"
"storm"
"father's joy, source of joy"
"light, illumination"
"from the alder grove"
"courageous, spirited"
Similar sound: These names share phonetic patterns with Rio — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Spanish/Portuguese origins, giving them the same cultural heritage as Rio.
Rhythm: Rio is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.