Chiefly The worst or least favourable condition, value, or amount. Opposed to optimum.
Chiefly Worst, least favourable, especially under a particular set of circumstances.
Early 19th century. From classical Latin pessimum lowest quality, worst condition, greatest detriment, use as noun of neuter of pessimus worst from the same base as pēior worse + -imus, extended form of suffix forming superlatives.