Compulsory \Com*pul"so*ry\, a. [LL. 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 compulsory. --Burke.

Source: Webster's Revised Unabridged Dictionary (1913)