Onyx sits next to 4 phonetic neighbors — Knox, Phoenix, and Felix are the closest matches by sound. Most share Onyx's Greek (onyx)-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"black gemstone"
"raven"
"thunder and lightning"
"hollow (place)"
"land where rye grows"
"peace town; settlement of peace"
"great king"
"strong, virtuous"
"little star"
"sun"
"king, master"
"young creature, cub"
"wave, abundant, learned"
"advice, counsel"
"wise person"
"son of Hendrik"
"descendant of Grádaigh"
"from the city of Milan"
"victory of the people (from Nicholas)"
"ever powerful"
"who is like God"
Similar sound: These names share phonetic patterns with Onyx — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Greek (onyx) origins, giving them the same cultural heritage as Onyx.
Rhythm: Onyx is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.