Glen sits next to 4 phonetic neighbors — Glenn, Glyn, and Bren are the closest matches by sound. Most share Glen's Scottish cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"narrow valley, mountain valley"
"Dack's settlement"
"with melody, melodious"
"son of the sea (via Dylan influence)"
"a crow-like black bird"
"immortal, deathless"
"invented modern name, no classical meaning"
"wealthy protector"
"God is gracious"
"cooked rice, meal"
"Brook land, land by the brook"
"crossroads, cross"
"keeper of enclosed parkland"
"heri (army) + beraht (bright)"
"light, pale"
"rain, precipitation"
"vigorous youth"
"village by the street"
"concluding musical passage"
"young warrior"
"rhythmic flow, musical cadence"
Similar sound: These names share phonetic patterns with Glen — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Scottish Gaelic origins, giving them the same cultural heritage as Glen.
Rhythm: Glen is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.