Sonder sits next to 4 phonetic neighbors — Sander, Sondar, and Thunder are the closest matches by sound. Most share Sonder's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"the realization that every stranger has a full and vivid life"
"playful one"
"permanent, long-lasting"
"virtuous, upright"
"from the Cassius Roman family clan"
"one who burns, charcoal burner, distiller"
"great one"
"son of the grey-haired one"
"one who rules"
"dwellers in wooded hills"
"modern Jax + Hebrew -iel (of God)"
"short form of Andre/Andrew"
"God the most high (via Omari)"
"of the river (if -von is from Welsh afon)"
"healing, remedying"
"thicket keeper"
"God is my judge (short form of Daniel)"
"gift of God"
"battle, spirit of battle"
"the king"
"elaborated form of Joshua"
Similar sound: These names share phonetic patterns with Sonder — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Neologism from German sonder + French sonder origins, giving them the same cultural heritage as Sonder.
Rhythm: Sonder is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.