monopoly: one seller, many buyers
duopoly: two sellers, many buyers
oligopoly: a few sellers, many buyers

monopsony: one buyer, many sellers
duopsony: two buyers, many sellers
oligopsony: a few buyers, many sellers

Th only way to sort out this buyer-seller business to me is to hang on to the word option.

c.1600, "action of choosing," from Fr. option, from L. optionem (nom. optio) "choice, free choice," related to optare "to desire, choose," from PIE base *op- "to choose, prefer." Meaning "thing that may be chosen" is attested from 1885. Commercial transaction sense first recorded 1755 (the verb in this sense is from 1934).