The antonyms for the word "act part" can vary depending on the context in which it is used. However, some common antonyms are "spectator," "observer," and "non-participant." These terms suggest a lack of engagement, involvement, or participation in an activity or event. For example, in a theater performance, a spectator might be someone who watches the play without taking part in it, while an actor would play an active part in the production. Similarly, in a political event, an observer might be someone who watches the proceedings without getting involved, while a person who takes an active role in the event would be considered a participant.