Decorous means behaving in a way that's proper, polite, and appropriate for the situation. When students maintain decorous behavior during a school assembly, they sit quietly, listen attentively, and show respect for the speakers. When dinner guests use decorous manners, they wait their turn to speak, use utensils correctly, and thank their hosts.

The word suggests matching your behavior to what the moment requires, with attention to dignity and formality. Playing and shouting might be perfectly fine at recess, but decorous behavior in the library means speaking softly and moving carefully. A decorous ceremony, like a graduation or memorial service, has a sense of dignity and formality that everyone respects.

The opposite is indecorous, meaning inappropriate or improper. Laughing loudly during a serious speech would be indecorous. Wearing pajamas to a wedding would be indecorous.

Think of decorous as the difference between knowing how to behave and actually choosing to behave that way when it matters. Someone who acts decorously understands that different situations call for different kinds of behavior, and adjusts accordingly.