compulsory

Definitions:

Not of choice; not voluntary; having the power to compel.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (adjective) (adj.) (adjective)
Compulsorily.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adverb) (adv.) (adverb)
Having power to compel; employing compulsion; enforced by compulsion.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (adjective) (adj.) (adjective)
Exercising force or restraint; enforced.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adjective) (adj.) (adjective)

Usage examples:

Since 1900 attendance at the primary schools between the ages of six and thirteen is compulsory
- History of Holland by George Edmundson
Statement by the home teacher working among these peasants: There ought to be schools to teach English to the parents at which their attendance would be compulsory
- A Stake in the Land by Peter Alexander Speek
If I had my way boxing would be compulsory by George!
- Left Tackle Thayer by Ralph Henry Barbour