Sentence:  Once <WSD>covertly</WSD> 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 not seeing the face of that vile creature . 
Meaning of the word marked with <WSD> tags:  in a covert manner