If you describe something as foul, you mean it is dirty and smells or tastes unpleasant.

Foul language is offensive and contains swear words or rude words.

If someone has a foul temper or is in a foul mood, they become angry or violent very suddenly and easily.

Foul weather is unpleasant, windy, and stormy.

If a place is fouled by someone or something, they make it dirty.

If an animal fouls a place, it drops faeces onto the ground.

If a machine or vehicle fouls part of its mechanism or if something such as a rope fouls the mechanism, the mechanism can no longer work properly because something has become twisted or knotted around it.

In a game or sport, if a player fouls another player, they touch them or block them in a way which is not allowed according to the rules.

A foul is an act in a game or sport that is not allowed according to the rules.

If you cry foul, you claim that someone, especially an opponent or rival, has acted illegally or unfairly.

If someone tries to achieve something by fair means or foul, they use every means possible in order to achieve it, and they do not care if their behaviour is dishonest or unfair.

If you fall foul of someone or run foul of them, you do something which gets you into trouble with them.

If you foul up something such as a plan, you spoil it by doing something wrong or stupid.