Kes sits next to 4 phonetic neighbors — Kez, Bess, and Tess are the closest matches by sound. Most share Kes's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"Rainbow; or kestrel bird"
Similar sound: These names share phonetic patterns with Kes — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Hebrew/English origins, giving them the same cultural heritage as Kes.
Rhythm: Kes is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.