Compulsory, a.
Etymology: [LL. compulsorius.]
1. Having the power of compulsion; constraining.
2. Obligatory; enjoined by authority; necessary; due to complusion. This contribution therestening fall infinitely short of their hopes, they soon made it compulsory. Burke.
Shades of meaning
Fernald has no entry of its own for compulsory; he lists it under absolute.
He lists it without comment; the entries above explain its neighbors.