plenum

[ plee-nuh m, plen-uh m ]
/ ˈpli nəm, ˈplɛn əm /

noun, plural ple·nums, ple·na [plee-nuh, plen-uh] /ˈpli nə, ˈplɛn ə/.

the state or a space in which a gas, usually air, is contained at a pressure greater than atmospheric pressure.
a full assembly, as a joint legislative assembly.
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.
the whole of space regarded as being filled with matter (opposed to vacuum).

Origin of plenum

1670–80; < Latin, neuter of plēnus full1, in the phrase plēnum (spatium) full (space)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

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British Dictionary definitions for plenum

plenum
/ (ˈpliːnəm) /

noun plural -nums or -na (-nə)

an enclosure containing gas at a higher pressure than the surrounding environment
a fully attended meeting or assembly, esp of a legislative body
(esp in the philosophy of the Stoics) space regarded as filled with matterCompare vacuum (def. 1)
the condition or quality of being full

Word Origin for plenum

C17: from Latin: space filled by matter, from plēnus full
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012