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"
"new house (place name)"
"diminutive of Scott"
"chariot boy"
"physician, healer"
"hollow land (alternative)"
"Yahweh saves"
"soaring vessel, sky wanderer (symbolic)"
"gift of God, God is salvation"
"coal town dweller"
"honorable, morally excellent"
"descendant of Riagán"
"one who works with books"
"of Dionysus, god of wine"
"from the west farm"
"oracle, mouth of the serpent"
"counsel, power"
"ruler of the people"
"people's champion, victorious one"
"that which is true or real"
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.