any of a number of small, parallel beams of timber, steel, reinforced concrete, etc., for supporting floors, ceilings, or the like.
verb (used with object)
to furnish with or fix on joists.

1325–75; Middle English giste < Old French < Latin *jacitum support, noun use of neuter of Latin jacitus (past participle of jacēre to lie), equivalent to jaci- variant stem + -tus past participle suffix

joistless, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
joist (dʒɔɪst)
1.  See also rolled-steel joist a beam made of timber, steel, or reinforced concrete, used in the construction of floors, roofs, etc
2.  (tr) to construct (a floor, roof, etc) with joists
[C14: from Old French giste beam supporting a bridge, from Vulgar Latin jacitum (unattested) support, from jacēre to lie]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

late 14c. (attested from 1294 in Anglo-L.), from O.Fr. giste "beam supporting a bridge" (Mod.Fr. gîte), noun use of fem. pp. of gesir "to lie," from L. jacere "to lie, rest," related to jacere "to throw" (see jet (v.)). Notion is of wooden beam on which boards "lie down."
Online Etymology Dictionary, © 2010 Douglas Harper
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Encyclopedia Britannica


ceiling or floor support in building construction. Joists-of timber, steel, or reinforced concrete-are laid in a parallel series across or abutting girders or a bearing wall, to which they are attached, usually by metal supports called joist hangers, or anchors

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
It should extend vertically through the subfloor and cross a joist or some
  other support to which it is bolted.
He took a comb from its niche behind a joist and gave her old coat a rubbing.
It is nailed or screwed to the subfloor and joist and driven horizontally with
  a punch or nail set.
The box must be attached directly to a ceiling joist, and anchored firmly so
  that the box cannot twist or pull loose.
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