This is what Wikipedia has to offer under "soviet republic":
A soviet republic (from Russian: Советская республика - Sovetskaya respublika, German: Räterepublik, French: République des conseils, Dutch: Radenrepubliek, Ukrainian: Радянська республіка, Belarusian: Савецкая рэспубліка, etc) is a republic in which the government is formed of soviets (workers' councils) and politics are based on soviet democracy.
Although the term is usually associated with Soviet member-states, it was not initially used to represent the political organisation of the Soviet Union, but merely a form of democracy.
There were several revolutionary workers' movements in various areas of Europe which declared independence under the name of a soviet republic in the immediate aftermath of the First World War.
Edith adds the link: https://en.wikipedia.org/wiki/Soviet_republic...
I suppose the Soviet Union was originally a soviet republic.