Cooper sits next to 3 phonetic neighbors — Harper, Hooper, and Jasper are the closest matches by sound. Most share Cooper's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"barrel maker, cask maker"
"royal woodland clearing"
"new (naval)"
"endurance, patient suffering"
"bright, shining light"
"child of the earth"
"feminine elaboration of George"
"resurrection (via Anastasia)"
"modern coined name"
"gracious, dear one"
"goddess of the hunt"
"each of the two, pure"
"heather plant (Calluna vulgaris)"
"meadow, clearing"
"alert, watchful"
"soft, tender"
"mountain nymph"
"precipitation, water from the sky"
"beloved, cherished"
"rain (weather)"
Similar sound: These names share phonetic patterns with Cooper — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Middle English origins, giving them the same cultural heritage as Cooper.
Rhythm: Cooper is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.