Sentence:  Once covertly looking at Simms Purdew , the only man in the world whom he hated , he had seen the heavy , slack , bestubbled jaw open and close to emit the cruel , obscene banter , and had seen the pale blue eyes go watery with whisky and merriment , and suddenly he was <WSD>not</WSD> seeing the face of that vile creature . 
Meaning of the word marked with <WSD> tags:  negation of a word or group of words