1.
strange smell; foul odor; stench
An unusual or unpleasant smell that is out of the ordinary. Often used to report suspicious or alarming odors, such as gas leaks, chemical spills, or decomposition.
Usage
異臭 is commonly found in news reports and official communications. The most typical pattern is 異臭がする (there is a strange smell).
Unlike 臭い, which can be neutral (any smell), 異臭 always implies something abnormal and usually unpleasant. It often signals danger or something requiring investigation.