I. ˈplenəm, -lēn- noun
( plural plenums -mz ; or plena -nə)
Etymology: New Latin, from Latin, neuter of plenus full — more at full
1.
a. : a space or all space every part of which is full of matter — opposed to vacuum
b.
(1) : a condition in which the pressure of the air in an enclosed space is greater than that of the outside atmosphere
(2) : an enclosed space in which such a condition exists ; especially : a plenum chamber
2.
a. : a general assembly of all members especially of a legislative body
b. : the entire membership of a specific group
3. : the quality or state of being full
II. adjective
: relating to or being a space in which a plenum exists
a plenum chamber in a hot-air furnace
the plenum system forces air into the room, causing a leakage outward although exhaust ducts may also be provided — V.M.Ehlers & E.W.Steel