• WordNet 3.6
    • v underact act (a role) with great restraint
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Webster's Revised Unabridged Dictionary
    • v. t Underact To perform inefficiently, as a play; to act feebly.
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Century Dictionary and Cyclopedia
    • underact To act or perform, as a play or part, inefficiently.
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Chambers's Twentieth Century Dictionary
    • v.t Underact un-dėr-akt′ to act a part inefficiently
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In news:

An underactive thyroid can cause symptoms like those of depression or menopause.