Where does “Fitzwilliam” come from?

Fitzwilliam is an English surname combining the Old French fitz (son of) with the personal name William, ultimately derived from Latin filius (son) and Proto-Indo-European dʰeh₁y-li-os.

Ancestry of “Fitzwilliam”, step by step

Step	Language	Word	Meaning
1	English	Fitz-	Son of; especially used for the illegitimate sons...
2	Anglo-Norman	fitz	Alternative form of filz
3	Old Irish	du-	—
4	Sicilian	di	—
5	Latin	dē	—
6	Latin	post	behind; after, since, besides, except; behind,...
7	Latin	poste	ablative singular of postis
8	Proto-Italic	posti	—
9	Proto-Indo-European	pósti	—
10	Proto-Indo-European	pós	afterwards, post; by, at

Every word from Proto-Indo-European pós →

Fitzwilliam — Etymology, Origin & Word History | Etymology Explorer