Sentence:  Lawrence Lipton , in The Holy Barbarians , stresses that for the beat generation sex is more than a source of pleasure ; it <WSD>is</WSD> a mystique , and their private language is 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:  be identical to; be someone or something