Frederick sits next to 4 phonetic neighbors — Friedrich, Fredrik, and Federico are the closest matches by sound. Most share Frederick's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"peaceful ruler"
"battle, warrior spirit"
"from Brix (place name)"
"from Laurentum, laurel-crowned"
"son of Andrew (manly)"
"crown, wreath"
"red (hair color)"
"healer, physician"
"south Munster (place name)"
"divinely appointed, called by God"
"healer (if derived from Jason/Kason)"
"ardor, enthusiasm, fierceness"
"substitute, replacement"
"God is gracious"
"rest, repose"
"strong, virtuous"
"little battle"
"rock, stone"
"strong ruler, powerful leader"
"born of fire"
"God has heard"
Similar sound: These names share phonetic patterns with Frederick — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Germanic origins, giving them the same cultural heritage as Frederick.
Rhythm: Frederick is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.