means The tendency to expect the worst outcome or to dwell on the negative side of things.

from From Latin 'pessimus,' meaning 'worst' — the superlative of 'malus,' 'bad.' It was deliberately coined as the dark twin of 'optimism' (from 'optimus,' 'best'), the two words entering European philosophy together in the 18th century as people argued over whether this was the best or worst of all possible worlds. So 'pessimism' is, quite literally, the doctrine of the worst.