(sociolinguistics) A language user's grammatical knowledge of syntax, morphology, phonology and the like, as well as social knowledge about how and when to use utterances appropriately.

(communism, history) The economic policy of the RSFSR during the Russian Civil War.

plural of people's commune

An administrative level in rural areas of the People's Republic of China from 1958 to 1983.

(derogatory, politics) Yugoslavian socialism when viewed as a Serb political ideology.

plural of house-commune

A communal housing structure built as part of an architectural and social movement in the Soviet Union in the 1920–1930s.

plural of communicating vessel

(physics, used mostly in plural) One vessel in a system of containers filled with a homogeneous fluid, connected at the base and subjected to the same atmospheric pressure.

plural of intelligence community