anti-monarchical
adjective
an·ti-mo·nar·chi·cal 
ˌan-tē-mə-ˈnär-ki-kəl,
-mä-,
ˌan-tī- variants or less commonly antimonarchical
: opposed to or hostile toward monarchies or monarchs : anti-monarchist
an anti-monarchical revolution
Word History
First Known Use
1641, in the meaning defined above