Onix sits next to 4 phonetic neighbors — Onyx, Phoenix, and Felix are the closest matches by sound. Most share Onix's Spanish-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"black banded gemstone"
"descendant of Raghallach"
"son of the home ruler"
"hospitality toward strangers"
"marked one"
"Creative African American name; strong and distinctive"
"life, living existence"
"triumph, conquest"
"who is like God? (rhetorical, meaning no one)"
"deep valley dweller"
"small songbird, finch"
"the third (in family lineage)"
"son of the sea"
"one who climbs to great heights"
"red-haired one"
"from the fortress"
"from the Bexton place"
"god-helmet, protected by divinity"
"knife, cutler"
"modern invented combination of grey + len"
"combination of strong/complete and my God is Yahweh"
Similar sound: These names share phonetic patterns with Onix — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Greek origins, giving them the same cultural heritage as Onix.
Rhythm: Onix is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.