fast and slow

Fast and slow are opposites describing speed or rate.

Fast means quick, rapid, or happening in little time: a fast car, fast reflexes.

Slow means unhurried, taking more time than expected: slow progress, a slow learner.

Both work as adjectives and adverbs—you can drive fast or drive slow, though slowly remains the formal adverb.

A fast friend is loyal and steadfast, from an older sense of firmly fixed.

A clock running fast shows a later time than actual; running slow, an earlier time.