The phrase "slightest whiff" refers to the smallest or faintest hint or trace of something, usually a smell or indication of a specific thing. Full definition
Unfortunately, human beings only grow when there is a slight whiff of danger in the air. (entrepreneur.com)
It's a slight whiff of euphoria around the stock market rally, the first time I have smelled it in a long time. (cnbc.com)
Prime Minister Justin Trudeauâ $ ™ s speeches both in the House Monday afternoon, and at the vigil that evening, bore more than a slight whiff of greasepaint. (insightalberta.ca)