An act , in the sense considered here, is something that is done. The act may be done by a person, a group or an impersonal entity, and is not limited by motive, nature or result. Thus, an act of God is a violent outbreak of nature; the act of a maniac may endanger the community; the act of a philanthropist may enrich it. While act refers to something that is accomplished, action refers to the accomplishing of it or the process by which it is accomplished: the action of acid on metal.

Deed , while sometimes used to connote any act , good or bad, big or small, is usually synonymous with exploit and feat in meaning an achievement of great courage, nobility, intelligence, strength or skill. An exploit is often a physical act ; discovering a continent, scaling a high mountain, rocketing to a distant planet, and descending to the ocean floor are all exploits . A feat may also be a physical act , but it applies to mental acts as well.

• Formulating the General Theory of Relativity was a prodigious mental feat ; Playing several chess games simultaneously while blindfolded is a remarkable and impressive feat .

A deed is generally an act that is noteworthy for its difficulty or nobility.

• The labours of Hercules were deeds of courage and ingenuity; A good deed may range from endowing a university to helping an old lady cross the street.

Operation and performance in this context can be synonymous with act or action , but are usually considered to be combinations of acts or the manner in which they are carried out. A military operation is a series of co-ordinated individual and group acts ; the performance of an employee is the manner in which he carries out the acts that are part of his job’s routine.