If you say that someone is a master craftsman you mean that they are extremely skilled at that activity. If you say that someone is, for example, a master builder or a master carpenter, you mean that they are fully qualified to practise their trade and to train others in it.

A master copy of something, such as a film or a tape recording, is an original copy that can be used to produce other copies.

A servant's master is the man that he or she works for.

If you say that someone is a master of a particular activity, you mean that they are extremely skilled at it.

If you are master of a situation, you have complete control over it.

A famous male painter of the past is often called a master.

A master's degree can be referred to as a master's.

If you master something, you learn how to do it properly or you succeed in understanding it completely.

If you master a difficult situation, you succeed in controlling it.