Onslow sits next to 4 phonetic neighbors — Anslow, Enslow, and Onslo are the closest matches by sound. Most share Onslow's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"Ōn's hill; from the hill of Ōn"
"manly, brave"
"lord of the right path"
"work-power, home-ruler"
"to tame, subdue"
"gracious defender (if related to Desmond)"
"descendant of the champion"
"ruler of the people"
"Leaseholder; tenant farmer"
Similar sound: These names share phonetic patterns with Onslow — 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 Onslow.
Rhythm: Onslow is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.