English▸ 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).