Fitzwilliam sits next to 4 phonetic neighbors — William, Fitzgerald, and Fitzroy are the closest matches by sound. Most share Fitzwilliam's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"son of William"
"from the fortress town"
"the greatest"
"the praised one"
"counsel meadow"
"of noble kind"
"abundant forest or precious jade"
"one who listens intently, listener"
"from the clay valley"
"village at the ford; river-crossing settlement"
"God ruler; one who rules with divine authority"
Similar sound: These names share phonetic patterns with Fitzwilliam — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Anglo-Norman origins, giving them the same cultural heritage as Fitzwilliam.
Rhythm: Fitzwilliam is a 4-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.