Zillion sits next to 4 phonetic neighbors — Dillion, Killian, and Gillian are the closest matches by sound. Most share Zillion's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"an extremely large, uncountable number; boundless"
"fire and blood (fictional Valyrian)"
"dark foreigner; dark stranger"
"old river; slow-flowing water"
"dawn, morning"
"noble estate"
"craftsman, carpenter"
"strong as a wild boar"
"very blessed, very holy"
"from the valley"
Similar sound: These names share phonetic patterns with Zillion — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have English origins, giving them the same cultural heritage as Zillion.
Rhythm: Zillion is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.