obligatory
adjective uk/əˈblɪɡ.ə.tər.i/ us/əˈblɪɡ.ə.tɔːr.i/
C1 （根据规定、法律等）必须履行的，强制性的，有义务的
If something is obligatory, you must do it because of a rule or law, etc.
The medical examination before you start work is obligatory. 工作前必须先体检。
[ + to infinitive ] The statute made it obligatory for all healthy males between 14 and 60 to work. 这条法令规定所有年龄在14至60岁的男子必须工作。
C2 （因为常发生而）必然的，预料之中的;惯常的
expected because it usually happens
Several Secret Service agents surrounded the President, all wearing the obligatory raincoat and hat. 几名特工围在总统四周，当然是一律穿着风雨衣，戴着帽子。