Wiktionary
n. An economic condition in which a small number of buyers exert control over the market price of a commodity.
Wikipedia
An oligopsony (from Ancient Greek ὀλίγοι (oligoi) "few" + ὀψωνία (opsōnia) "purchase") is a market form in which the number of buyers is small while the number of sellers in theory could be large. This typically happens in a market for inputs where numerous suppliers are competing to sell their product to a small number of (often large and powerful) buyers. It contrasts with an oligopoly, where there are many buyers but few sellers. An oligopsony is a form of imperfect competition.
The terms monopoly (one seller), monopsony (one buyer), and bilateral monopoly have a similar relationship.
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oligopsony