Sidney sits next to 3 phonetic neighbors — Sydney, Cindy, and Sadie 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
"wide island"
"of the Kiani dynasty, noble"
"star of the sea, beautiful"
"God will provide"
"heavenly mist"
"light is mine"
"wealthy in battle"
"of the Aryan/Indo-Iranian people"
"full of life"
"she-god, divinity (Phoenician interpretation)"
"named after the city, place of red rocks"
"citadel, fortress"
"beautiful sky"
"grace, favor"
"bright, sparkling (phonetic association)"
"woman of the tribe"
"entire, complete"
"from Hadria (short for Adriaan)"
"lovable"
"immortal, eternal"
Similar sound: These names share phonetic patterns with Sidney — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Old English 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.