What is the meaning of the word "act"?

Definitions:

a manifestation of insincerity noun
- They put on quite an act for your benefit.
a short theatrical performance that is part of a longer program noun
- The troupe did their act three times every evening.
to be suitable for theatrical performance verb
- This scene acts well.
to behave in a certain manner verb
- Stop acting like a dunce.
to behave unnaturally or affectedly verb
- You're just acting.
to discharge one's duties verb
- They acted as the chair for the duration of the meeting.
to have an effect or outcome verb
- The alarm system acts as a theft deterrent.
to perform an action verb
- I acted out last night's events.
to perform on a stage or theater verb
- We act in this play.
to play a role or part verb
- I am acting in the play all week.
to pretend to have certain qualities or state of mind verb
- We acted the idiot.