plenum
n. countablen. a meeting where everyone in a group is present. It can also mean a space that is completely full of something, like air or gas.
n. a meeting of an entire body or assembly; also, a chamber or space filled with a fluid or gas. Often used in technical contexts to describe a volume of air or a full assembly of delegates.
The committee will discuss the proposal in a plenum tomorrow.
After the breakout sessions, all the delegates gathered in the main hall for a plenum to vote on the final report.
The physicist explained that the experiment required a vacuum, as the presence of air in the plenum would interfere with the delicate measurements of the particle's trajectory.
From Latin plēnum n (“space filled with matter”), from plēnus (“full”). The sense of "legislative meeting" is a semantic loan from Russian пле́нум (plénum, “plenary session”), from the same Latin source.