Sentence:  The Greek evidently fell for her , `` Monsieur X '' recounted , and to clinch what he thought <WSD>was</WSD> an affair in the making he gave her 100000 francs ( about $ 300 ) and led her to the roulette tables . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)