Sentence:  Lawrence Lipton , in The Holy Barbarians , stresses that for the beat generation sex is more than a source of pleasure ; it is a mystique , and their private language <WSD>is</WSD> rich in the multivalent ambiguities of sexual reference so that they dwell in a sexualized universe of discourse . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)