Sentence:  The gym teacher left that year, his successors had no interest in boxing, and society soon passed into a zone where the idea of thirteen-year-old boys punching each other's faces for educational purposes became as unthinkable as the dense <WSD>fug</WSD> of tobacco smoke in our school's staff room. 
Meaning of the word marked with <WSD> tags:  A heavy, musty, and unpleasant atmosphere, usually in a poorly-ventilated area.