Sentence:  The humor of my proposition appealed more strongly to Miss Trevor than I had looked for, and from that time forward she became her old self again;.... Now she had come to look upon the matter in its true proportions, and her anticipation of a <WSD>possible</WSD> chance of teaching him a lesson was a pleasure to behold. 
Meaning of the word marked with <WSD> tags:  Able but not certain to happen; neither inevitable nor impossible.