Sydni sits next to 3 phonetic neighbors — Sydney, Cindy, and Sidnie are the closest matches by sound. Most share Sydni's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"Wide meadow or wide island"
"flame, hill"
"first-born daughter"
"elf ruler (alternative folk etymology)"
"pearl"
"follower of Christ"
"God will add; gracious"
"defender of the people (from Greek roots of Lex)"
"noble kind, noble type"
"gift of God"
"royal clearing, king's wood"
Similar sound: These names share phonetic patterns with Sydni — 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 Sydni.
Rhythm: Sydni is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.