1) Aggressive 2) Armed 3) Binding 4) De rigueur 5) Enforced 6) Essential 7) Forced 8) Imposed 9) Mandatory 10) Necessary 11) Obligatory 12) Required 13) Required by rule 14) Requisite 15) Violent 1) Coactive 2) Compulsive 3) Essential 4) Forced 5) Mandatory 6) Necessary 7) Obligatory 8) Required 
• (a.) Obligatory; enjoined by authority; necessary; due to compulsion. • (a.) Having the power of compulsion; constraining.
[Adjective] Something that has to happen or that you must do.
Com·pul'so·ry adjective [ Late Latin compulsorius .] 1. Having the power of compulsion; constraining. 2. Obligatory; enjoined by authority; necessary; due to compulsion. « This contribution threatening to fall infinitely short of their hopes, they soon made it compuls...
[adj] - required by rule
mandatory adjective required by rule; `in most schools physical education is compulsory`; `attendance is mandatory`; `required reading`
[SAT terms] required by rule required by rule[Literary terms] required by rule[Literary terms] required by rule