Sylvan sits next to 4 phonetic neighbors — Silvan, Sylvio, and Ivan are the closest matches by sound. Most share Sylvan's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"of the forest, woodland"
"servant, worshipper of God"
"he judged, he governed"
"supplanter, one who follows at the heel"
"from Scotland, Scotsman"
"hazel valley dweller"
"flowing water, river"
"nonconformist, free spirit"
"greatest stream (via Maxwell)"
"hollow, empty"
"darling, beloved"
"helped by God, God has helped"
"counselor, advisor"
"cowherd's descendant"
"follower of Calvin (in Protestant tradition)"
"son of the earth-man"
"one touched by good fortune"
"elf counsel, wise counselor"
"peace, gentle"
"son of Jen (John)"
Similar sound: These names share phonetic patterns with Sylvan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin origins, giving them the same cultural heritage as Sylvan.
Rhythm: Sylvan is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.