adj

• (politics) Opposing a particular political party.
  "As in the whole country, cadres and poor and lower-middle peasants in our Taning County, inspired by the spirit of the National Conference on Learning From Tachai in Agriculture, were greatly stimulated and high in spirits and resolved to fight hard in the movement of learning from Tachai in agriculture and building Tachai-type counties everywhere. In the face of the excellent situation, the anti-party clique of the "gang of four,"--Wang, Chang, Chiang and Yao--stepped up their antiparty activities and strengthend their attacks on the party.[…] Today the party Central Committee headed by Chairman Hua Kuo-feng, carrying on the cause left behind by Chairman Mao and representing the basic interests of hundreds of millions of the revolutionary cadres and poor and lower-middle peasants, has smashed the intrigues of the antiparty clique of the "Gang of four" to usurp the party and seize power and sent the scoundrels--Wang Hung-wen, Chang Chun-chiao, Chiang Ching and Yao Wen-yuan--into the dock of history."

noun

• (politics) A political party that shuns or rejects the mainstream political establishment.
  "Differences arise over what kinds of organization are desirable (eg, political parties or antiparties, professionalized organizations, decentralized networks, communes, grassroots groups) and over tactical questions of what is to be done[…]"