Suddenly

google

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Middle English: from Anglo-Norman French sudein, from an alteration of Latin subitaneus, from subitus ‘sudden’.

wiktionary

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From Middle English sodenly, sodeynly, sodeinliche, sodaynlyche; equivalent to sudden +‎ -ly.

etymonline

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suddenly (adv.)

late 13c., sodeinli; see sudden + -ly (2).