obligatory
Pronunciation: /əˈblɪgət(ə)ri/
adjective
- required by a legal, moral, or other rule; compulsory: use of seat belts in cars is now obligatory
- (of a ruling) having binding force: a sovereign whose laws are obligatory
- often humorous so customary or fashionable as to be expected of everyone or on every occasion: it was a quiet little street with the obligatory pub at the end

Origin:
late Middle English: from late Latin obligatorius, from Latin obligat- 'obliged', from the verb obligare (see oblige)

Spelling help
The ending of obligatory is -ory.