Which adjective describes something that is harmful and deceitful?

The adjective "treacherous" is used to describe something that is not only harmful but also deceitful. It connotes a sense of betrayal or danger coming from an unexpected source. For example, a treacherous person might appear trustworthy but has ulterior motives that can cause significant harm. This word captures both the element of danger and the deceptive nature of a situation or individual.

The other adjectives do not fit this definition; "exhaustive" refers to something thorough and comprehensive, "wonderful" connotes positivity and delight, while "comfortable" relates to a sense of ease and relaxation. These words do not imply any harmful or deceitful qualities, which reinforces why "treacherous" is the most appropriate choice in this context.