Sidney sits next to 4 phonetic neighbors — Sydney, Sidney, and Cydney are the closest matches by sound. Most share Sidney's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"from Saint Denis"
"cross, crossroads"
"linden tree, lime tree"
"free man (via Carson)"
"serpent's mouth"
"river traveler"
"illuminance unit"
"modern creative name construction"
"youthful"
"Yahweh has given"
"modern invented name"
"salvation of God"
"son of Javan, modern invention"
"immortality, eternal life (symbolic)"
"dweller by the willow"
"worth, worthiness"
"broad valley"
"my God is help"
"born at dawn, of the light"
"deep gorge, ravine"
"God has remembered"
Similar sound: These names share phonetic patterns with Sidney — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Anglo-Norman French origins, giving them the same cultural heritage as Sidney.
Rhythm: Sidney is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.