IPA: /ˈɡɪl.tɪ.li/
KK: /ˈɡɪl.tɪ.li/
In a way that shows feelings of guilt or remorse.
She looked at him guiltily after breaking the vase.
Guiltily → It is formed from "guilt" (from Old English "gylt", meaning a crime or sin) and "-ily" (a suffix forming adverbs meaning in a manner). The word "guiltily" means in a manner that shows guilt or remorse.
Think of feeling guilty about a crime or sin ('guilt') and how you might act 'in a manner' ('-ily') that reflects that feeling.