A dog is a very common four-legged animal that is often kept by people as a pet or to guard or hunt. There are many different breeds of dog.

You use dog to refer to a male dog, or to the male of some related species such as wolves or foxes.

If someone calls a man a dog, they strongly disapprove of him.

People use dog to refer to something that they consider unsatisfactory or of poor quality.

If someone, especially a man, calls a woman or girl a dog, they mean that she is very ugly, unattractive, or boring.

If problems or injuries dog you, they are with you all the time.

The dogs is a sports meeting where dogs, especially greyhounds, race and people bet on which dog will win.

You describe something as a dog's breakfast or dog's dinner in order to express your disapproval of it, for example because it is very untidy, badly organized, or badly done.

You use dog eat dog to express your disapproval of a situation where everyone wants to succeed and is willing to harm other people in order to do so.

If you say that something is going to the dogs, you mean that it is becoming weaker and worse in quality.

If someone tells you to let sleeping dogs lie, they are warning you not to disturb or interfere with a situation, because you are likely to cause trouble and problems.

If you say 'You can't teach an old dog new tricks', you are suggesting that someone is unwilling to try new ways of doing things.