Underact v. t. : To perform inefficiently, as a play; to act feebly.

Example:
Do you think it is worse to overact or Underact?

Taxonomy
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Defination from the web:
underact from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... Learn more about "underact" Learn more about "underact" and related topics at Britannica.com. Pronunciation Symbols. Share this entry: Link to this page: ...