IPA: /ˈflɔːləsli/
KK: /ˈflɔːləsli/
In a way that is perfect and without any mistakes or faults.
She performed the dance flawlessly, impressing everyone in the audience.
Flawlessly → It is formed from "flaw" (from Old English *flāw*, meaning a defect or blemish) and the suffix "-less" (meaning without) and the adverbial suffix "-ly" (meaning in a manner). The word "flawlessly" means in a manner without defects or blemishes.
Think of being 'without' ('-less') any 'defects' ('flaw') — that's how you remember that 'flawlessly' means doing something perfectly.