Uniparty

Entry in progress—BP
 
Wiktionary: uniparty
Etymology
From uni- +‎ party.
Adjective
uniparty (not comparable)
1. (politics) Having only one political party, especially where opposition parties are outlawed; one-party, monoparty.
   
Politico
The Strange History of the ‘Uniparty’
Steve Bannon’s new buzzword has an interesting godfather: Ralph Nader.
By BEN ZIMMER November 17, 2017
(...)
But while “the Uniparty” may be trendy among the Breitbart set, it wasn’t born there. In fact, if you go back to the contentious presidential race of 2000, you’ll find it arose as a political barb among supporters of Ralph Nader, running as the nominee of the Green Party.
 
Numerous posts on the Usenet newsgroup alt.politics.green from that year railed against “the two-headed UniParty,” “the money-driven media/political uniparty environment,” “the corporate Uniparty grip on the civic polity,” and so forth.
 
Nader himself used the expression in his book “Crashing the Party,” reflecting on his experience running in 2000.