Sentence:  In theory , compulsive behavior is a way of diminishing anxiety , and one might expect a negative association except for the <WSD>possibility</WSD> that for many children the obsessive-compulsive defenses are not sufficient to quell the amount of anxiety they suffer . 
Meaning of the word marked with <WSD> tags:  a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena