The definition of mandatory is something that is required.
The definition of requisite is something required or necessary.
The definition of imperative is something that has authority or is absolutely necessary.
Declared by statute to be such, and hence legally punishable
The definition of binding is something that limits or holds someone to an agreement.
Required beforehand, esp. as a necessary condition for something following
Produced or kept up by unusual effort; not natural or spontaneous; strained or constrained
Imposed on one by authority, command, or convention
The definition of willing is agreeable do something.
Done or undertaken of one's own free will:
Having the power or authority to elect; electoral.
The definition of optional is available, but not required.
Empty or unoccupied:
Find another word for compulsory. In this page you can discover 28 synonyms, antonyms, idiomatic expressions, and related words for compulsory, like: compulsary, mandatory, requisite, imperative, obligatory, statutory, binding, prerequisite, unavoidable, required and non-compulsory.