Glenn sits next to 4 phonetic neighbors — Glen, Glynn, and Flynn are the closest matches by sound. Most share Glenn's Scottish cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"valley, narrow glen"
"immortality, eternal life (symbolic)"
"noble lord, feudal warrior"
"salvation of God"
"modern invented name"
"lord of the marches, borderlord"
"all wise (from Norse Alviss)"
"royal power, royal ruler"
"new house, bright"
"brave lion, lion-hearted"
"soaring, high-flying"
"son of Anne, son of Agnes"
"one who carves, wood-carver"
"winding river"
"Hawaiian form of Matthew"
"hound of the plain"
"salvation of the Lord (via Isaiah element)"
"built by the Lord"
"watchful, vigilant"
"mill town, settlement by the mill"
"of the Terentius clan"
Similar sound: These names share phonetic patterns with Glenn — 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 Glenn.
Rhythm: Glenn is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.