In a manner that shows you feel guilty or ashamed about something you did.
From guilty + -ly (adverb suffix forming adverbs from adjectives). The -ly suffix comes from Old English -lice, related to 'like' or 'manner', allowing adjectives to describe how actions are performed.
Guiltily is a perfect example of how English builds emotion into actions—when someone acts guiltily, their body language and tone reveal their conscience, which is why detectives watch for guilty behavior as much as guilty words.
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