IPA: /ˈsʌdənli/
KK: /sʌdənli/
Happening quickly and without warning.
The lights went out suddenly during the storm.
Suddenly → It is formed from "sudden" (from Middle English *sudden*, meaning unexpected or abrupt) and the adverbial suffix "-ly" (meaning in a manner of). The word "suddenly" means in a manner that is unexpected or abrupt.
Think of something happening in an unexpected way — that's what 'suddenly' means, as it describes an event occurring abruptly.