Compulsory
 Definition:  something that is required
  Synonyms:  Imperative, Mandatory, Obligatory, Required
  Antonyms:  Discretionary, Elective, Optional, Unimperative
 Definition:  something that is required
  Synonyms:  Imperative, Mandatory, Obligatory, Required
  Antonyms:  Discretionary, Elective, Optional, Unimperative