means A market dominated by a small handful of sellers, each so aware of the others that every move is a calculated stare-down.

from From Greek 'oligos' (few) plus 'polein' (to sell) — the same '-poly' you hear in 'monopoly,' where 'monos' means alone. So a monopoly is one seller, an oligopoly the few. The word is a modern coinage, built deliberately from those classical parts by economists wanting a name for the space between one seller and many.