Guilefully is an adverb that describes someone who is deceitful or tricky in their actions. Some synonyms for guilefully include deceitfully, slyly, cunningly, craftily, deviously, and artfully. These words all describe someone who is intentionally trying to trick or deceive others in order to achieve their goals. Another word with a similar meaning is insidiously, which implies a more subtle and gradual approach to deceit. All of these words carry a negative connotation, as they describe someone who is not truthful or honest in their actions. It is important to be cautious of those who act guilefully, and to seek out trustworthy individuals in your personal and professional life.