Definition of act out in English:

act out

Misbehave, especially when unhappy or stressed: many children who act out while awaiting placement in a health care facility end up in juvenile detention
More example sentences
  • If it thinks it is the dominant dog, it will also be stressed, and act out very negatively.
  • They need to know how to manage someone who is frustrated, who may not be able to communicate, and who will act out if they are unhappy.
  • He acts out aggressively as a response to being territorial (wanting to be the only one on a slide - or possessive - wanting a toy train all to himself).
See parent entry: act

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Pronunciation: ˌhjuːməˈrɛsk
noun
a short, lively piece of music