Obsidian sits next to 3 phonetic neighbors — Sebastian, Octavian, and Oberon are the closest matches by sound. Most share Obsidian's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"volcanic black glass"
"destroyer (possible etymological root)"
"keeper of the keys"
"fortunate protector"
"sea, ocean"
"God has heard (via Sam = Samuel)"
"friends, allies"
"to descend"
"one who makes wheels"
"paradise, divine realm"
"ford belonging to the king"
"the greatest, most excellent"
"slender, graceful"
"rising in the east; the hunter"
"son of James, supplanter"
"the best, most excellent"
"word, principle"
"swift as a deer"
"farm on the ridge"
"from Arles (city in France)"
"he will judge"
Similar sound: These names share phonetic patterns with Obsidian — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin origins, giving them the same cultural heritage as Obsidian.
Rhythm: Obsidian is a 4-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.