An Etymological Dictionary of Astronomy and Astrophysics

Required by law or a rule; obligatory; involving or exercising compulsion; coercive (OxforddDctionaries.com).

Etymology (EN): From M.L. compulsorius, from L. compulsus, p.p. of compellere, → compel.

Etymology (PE): Adjective from vâdâreš, vâdârkard, → compulsion.