Sydney sits next to 3 phonetic neighbors — Cindy, Cydney, and Sidney are the closest matches by sound. Most share Sydney's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"wide island; broad river-island"
"dweller at the hall"
"trio, the number three"
"heavenly, of the sky"
"of noble birth"
"crown, garland"
"the loved one"
"bitter, from Latin amara"
"gracious, youthful"
"helmeted chief"
"short form of Giovanna or Gianna"
"earth"
"beautiful one, noble"
"moon goddess"
"fate, predetermined course"
"goddess of the moon"
"divine messenger"
"little one, darling"
"bitter"
"industrious, striving"
"merciful, gracious"
Similar sound: These names share phonetic patterns with Sydney — 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 Sydney.
Rhythm: Sydney is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.