obligatory

Từ điển Oxford Advanced Learner 8th

ob·liga·tory BrE [əˈblɪɡətri] NAmE [əˈblɪɡətɔːri] adjective
1. ~ (for sb) (to do sth) (formal)that you must do because of the law, rules, etc.
Syn: ↑compulsory
•It is obligatory for all employees to wear protective clothing.
Opp: ↑optional
2. (often humorous)that you do because you always do it, or other people in the same situation always do it
•In the mid 60s he took the almost obligatory trip to India.

Word Origin:
[obligatory] late Middle English: from late Latin obligatorius, from Latin obligat- ‘obliged’, from the verb obligare, from ob- ‘towards’ + ligare ‘to bind’.

Example Bank:
•It's almost obligatory to have a blog nowadays.
•The college authorities have now made these classes obligatory.
•Recently safety regulations have made it obligatory for all competitors to wear fist protectors.
•The hotel has a terrace with comfy chairs for that obligatory cocktail.