English word sudden comes from Vulgar Latin subitanus

Detailed word origin of sudden

Dictionary entry	Language	Definition
subitanus	Vulgar Latin (la-vul)
subdain	Old French (842-ca. 1400) (fro)
sodein	Anglo-Norman (xno)
sodain	Middle English (1100-1500) (enm)
sudden	English (eng)	(poetic) Suddenly. (obsolete) Hastily prepared or employed; quick; rapid.. (obsolete) Hasty; violent; rash; precipitate.. Happening quickly and with little or no warning. (obsolete) An unexpected occurrence; a surprise.