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"
"from Airelle (Norman place name)"
"king, royal"
"friend"
"son of Maurice"
"rejoice, delight"
"love"
"muddy farm or settlement"
"old friend"
"lion-hearted, brave"
"fifth born"
"counselor, advisor"
"Yahweh has given"
"beautiful valley"
"flower (disputed folk etymology)"
"boundary gate"
"joy, happiness"
"held by the heel"
"little dark one"
"elder, respected one"
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.