Real Dictionary

action
An action movie is a film in which a lot of dangerous and exciting things happen. An action hero is the main character in one of these films.
If you action something that needs to be done, you deal with it.
The fighting which takes place in a war can be referred to as action.
countable noun: An action is something that you do on a particular occasion.
countable noun: To bring a legal action against someone means to bring a case against them in a court of law.
singular noun: The action is all the important and exciting things that are happening in a situation.
uncountable noun: Action is doing something for a particular purpose.
uncountable noun: The action of a chemical is the way in which it works, or the effects that it has.

ACTION in American English
a federal agency established in 1971 to supervise all U.S. government programs and agencies for volunteers, as the Peace Corps, VISTA, etc.
the doing of something; state of being in motion or of working
noun: an independent agency created by the US government in 1971 to administer domestic volunteer programs
noun: the process or state of acting or of being active