Sentence:  It <WSD>is</WSD> no coincidence that the hebephrenic patient , the most severely dedifferentiated of all schizophrenic patients , shows , as one of his characteristic symptoms , laughter - laughter which now makes one feel scorned or hated , which now makes one feel like weeping , or which now gives one a glimpse of the bleak and empty expanse of man 's despair ; and which , more often than all these , conveys a welter of feelings which could in no way be conveyed by any number of words , words which are so unlike this welter in being formed and discrete from one another . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)