Sentence:  Our next task is to consider the change in the amount of a commodity purchased when the market changes from an indefinitely large number of competing buyers to a single buying agency. This may be described as the comparison between competitive and <WSD>monopsony</WSD> buying, just as the corresponding comparison for selling was called the comparison between competitive and monopoly output. 
Meaning of the word marked with <WSD> tags:  A market situation in which there is only one buyer for a product; also, such a buyer. (from 1930s)