IPA: /ˌæn.ti.sʌbˈvɜːr.ʒən/
KK: /æntiˈsʌbˌvɜrʒən/
Opposing or acting against efforts to undermine or overthrow a system, especially in a political context.
The government implemented antisubversion measures to protect national security.
Antisubversion is formed from "anti-" (meaning against) and "subversion" (from Latin "subvertere", meaning to overturn or undermine). The word describes actions or ideologies that are against the act of undermining or overthrowing established systems or authorities.
Think of being 'against' ('anti-') something that 'overturns' ('subvertere') — that's why antisubversion means opposing efforts to undermine.