Sentence:  When in <WSD>one</WSD> letter Jessica informed me that her father did not like the idea of her going out alone on New Year's Eve , I knew for a moment an immense relief ; but the letter went on : she had cried , she had implored , she had been miserable at his refusal , and finally he had relented - and now how happy she was , how expectant ! 
Meaning of the word marked with <WSD> tags:  having the indivisible character of a unit