Sonia sits next to 4 phonetic neighbors — Sonya, Sofia, and Sophia are the closest matches by sound. Most share Sonia's Russian-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"wisdom"
"shadow, shade (if derived from Hebrew Zillah)"
"she who brings happiness"
"from the kingdom of Lothar"
"bird"
"smiley, cheerful one"
"holly tree settlement"
"bright, clear, famous"
"ardor, enthusiasm, passion"
"maiden, daughter"
"royal woodland clearing"
"flower, blossom, radiance"
"little Joss, playful one"
"cushion, pillow"
"rose lake, rose by the water"
"famous warrior with brightness"
"young one, puppy (young animal)"
"from the church, basilica"
"judged, vindicated"
"standing up again, rebirth"
"cheerful"
Similar sound: These names share phonetic patterns with Sonia — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Greek via Slavic origins, giving them the same cultural heritage as Sonia.
Rhythm: Sonia is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.