com·pul·so·ry /kəm-'pəl-sə-rē/ adj
1: required or compelled by law: mandatory obligatory
compulsory insurance; specif: required to be brought or asserted in a pleading because of having arisen from the transaction or occurrence that is the subject of litigation
a compulsory counterclaim
2: using compulsion: compelling
compulsory measures
com·pul·so·ri·ly /-sə-rə-lē/ adv
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.