Sentence:  In thinly-peopled spots, I have known brick-layers on tramp, coming up with bricklayers at work, to be so sensible of the <WSD>indispensability</WSD> of lookers-on, that they themselves have sat up in that capacity, and have been unable to subside into the acceptance of a proffered share in the job, for two or three days together. 
Meaning of the word marked with <WSD> tags:  The characteristic of being indispensable.