Definitions:

1. Morally or legally constraining or binding. ADJECTIVE
   • Paying taxes is an obligatory civic duty for all citizens.
2. Required by law, rule, custom, or duty. ADJECTIVE
   • Wearing seat belts is obligatory in most countries.
3. Something that is required or mandatory due to either legal, etical, or moral rules and regulations. ADJECTIVE
   • It is obligatory for doctors to maintain patient confidentiality.

Synonyms:

• binding
• compulsory
• mandatory
• required
• unavoidable