obligatory
US /əˈblɪɡ.ə.tɔːr.i/
UK /əˈblɪɡ.ə.tɔːr.i/
1.
required by a legal, moral, or other rule; compulsory.
:
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It is obligatory for all students to wear uniforms.
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Attendance at the meeting is obligatory for all staff.
2.
(of a person or their behavior) done to conform to social or legal requirements rather than from genuine desire or interest.
:
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He gave an obligatory smile, clearly not amused.
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The polite applause was merely obligatory.