Real Dictionary

compulsory
adjective: If something is compulsory, you must do it or accept it, because it is the law or because someone in a position of authority says you must.

compulsory in American English
that must be done, undergone, etc.; obligatory; required
adjective: required; mandatory; obligatory
noun: something, as an athletic feat, that must be performed or completed as part of a contest or competition

compulsory in British English
adjective: required by regulations or laws; obligatory