Allan sits next to 4 phonetic neighbors — Alan, Allen, and Alvin are the closest matches by sound. Most share Allan's Scottish cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"rock, harmony"
"triumphant, victorious"
"pure, without blemish"
"speckled, freckled"
"good man, strong man"
"faithful, loyal, trustworthy"
"great chief, eminent lord"
"stone clearing, rocky glade"
"herb garden settlement"
"from the River Clyde"
"western clearing"
"son of Aodh (fire)"
"God knows"
"courteous, well-bred"
"agreement to stop fighting, temporary peace"
"lisping"
"great one"
"valley, dell"
"God is salvation"
"generous, noble, honorable"
"dark settlement"
Similar sound: These names share phonetic patterns with Allan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Celtic/Brythonic origins, giving them the same cultural heritage as Allan.
Rhythm: Allan is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.