the state or a space in which a gas, usually air, is contained at a pressure greater than atmospheric pressure.
2.
a full assembly, as a joint legislative assembly.
3.
a space, usually above a ceiling or below a floor, that can serve as a receiving chamber for air that has been heated or cooled to be distributed to inhabited areas.
4.
the whole of space regarded as being filled with matter (opposed to vacuum).
Origin
1670-80; < Latin, neuter of plēnusfull, in the phrase plēnum (spatium) full (space)
Examples from the web for plenum
He had left the world a plenum, and he now finds it a vacuum.
Large eddy simulation of thermal jets injected into a plenum mockup.
Electrical wiring will not be permitted in the plenum space in either case.
Makeup air was pushed unrestricted into the plenum over the worker's head.
British Dictionary definitions for plenum
plenum
/ˈpliːnəm/
noun (pl) -nums, -na (-nə)
1.
an enclosure containing gas at a higher pressure than the surrounding environment
2.
a fully attended meeting or assembly, esp of a legislative body
3.
(esp in the philosophy of the Stoics) space regarded as filled with matter Compare vacuum (sense 1)
4.
the condition or quality of being full
Word Origin
C17: from Latin: space filled by matter, from plēnus full
Word Origin and History for plenum
n.
1670s, "filled space" (opposite of vacuum), from Latin plenum (spatium) "full (space)," neuter of adjective plenus "complete, full" (see plenary). The meaning "of a full assembly of legislators" is first recorded 1772.