Sentence:  And listening to such a conversation <WSD>one</WSD> morning while taking a cup of chocolate in a cafe , Rousseau found himself bathed in perspiration , trembling lest his authorship become known , and at the same time dreaming of the startling effect he would make if he should proclaim himself suddenly as the composer . 
Meaning of the word marked with <WSD> tags:  having the indivisible character of a unit