Bertram sits next to 4 phonetic neighbors — Bertrand, Bertrum, and Barton are the closest matches by sound. Most share Bertram's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"bright raven"
"variant of Adrian"
"bright raven"
"Beautiful; lovely"
"Sun; throne - from Old Persian Kurush meaning one who bestows care"
"defender of men"
"brave, daring"
"rosemary (when short for Rosemary)"
"to pass over, to spare"
"time, era, eternity"
"rough clearing or rough woodland clearing"
Similar sound: These names share phonetic patterns with Bertram — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Old High German beraht + hraban origins, giving them the same cultural heritage as Bertram.
Rhythm: Bertram is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.