Sudden
Middle English: from Anglo-Norman French sudein, from an alteration of Latin subitaneus, from subitus ‘sudden’.
wiktionary
From Middle English sodeyn, sodain, from Anglo-Norman sodein, from Old French sodain, subdain(“immediate, sudden”), from Vulgar Latin *subitānus(“sudden”), from Latin subitāneus(“sudden”), from subitus(“sudden", literally, "that which has come stealthily”), originally the past participle of subīre(“to come or go stealthily”), from sub(“under”) + īre(“go”). Doublet of subitaneous.
etymonline
sudden (adj.)
early 14c., sodaine, from Anglo-French sodein or directly from Old French sodain, subdain "immediate, sudden" (Modern French soudain), from Vulgar Latin *subitanus, variant of Latin subitaneus "sudden," from subitus past participle of subire "go under; occur secretly, come or go up stealthily," from sub "up to" (see sub-) + ire "come, go" (from PIE root *ei- "to go"). "The present spelling was not finally established till after 1700" [OED].
Noun meaning "that which is sudden, a sudden need or emergency" is from 1550s, obsolete except in phrase all of a sudden first attested 1680s, also of a sudayn (1590s), upon the soden (1550s). Sudden death, tie-breakers in sports, first recorded 1927; earlier in reference to coin tosses (1834). Related: Suddenness.
