Theseus sits next to 4 phonetic neighbors — Perseus, Orpheus, and Proteus are the closest matches by sound. Most share Theseus's Greek-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"to set, to place, to establish"
"friend, companion"
"father, head of monastery"
"son of Aodh (fire)"
"high place, island"
"of the earth mother"
"narrow strait, channel"
"lyric poetry, song set to the lyre"
"farmer, steward of land"
"modern coinage"
"wayfarer, wanderer"
"young wolf"
"holder of the heel, supplanter"
"gift of Isis"
"split, torn apart"
"God enlightens"
"son of Ay, moon's son (via Turkish)"
"gift of God"
"marshland meadow"
"the Lord is salvation"
"hedgerow, boundary"
Similar sound: These names share phonetic patterns with Theseus — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Ancient Greek origins, giving them the same cultural heritage as Theseus.
Rhythm: Theseus is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.