Compulsorily comes from compulsory + -ly. Compulsory derives from Medieval Latin compulsorius, from compulsus, past participle of compellere ('to force'), from com- ('together') + pellere ('to drive'). The historical trail runs through compulsorius in Latin and pellere in Latin. Morphologically, compulsorily is transparent: it draws on compulsory + -ly. Used as an adverb, compulsorily now means "in a way that is required by law or rule; obligatorily", so the present definition can be read against the older forms and meanings. The same lexical family is also visible in related forms such as compulsory, compulsion, and compel. The result is a borrowed or transmitted form whose modern spelling carries a compact record of its route into English.