WordNet: obligatory

morally or legally constraining or binding; "attendance is obligatory"; "an obligatory contribution"

• also see necessary

• similar to bounden

• similar to compulsory, mandatory, required

• similar to de rigueur

• similar to imposed

• similar to incumbent on

• similar to indispensable

• similar to prerequisite

obligatory

• (englanti) optional (antonym)
• (suomi) pakollinen (synonyymi)