Definition of joist noun from the Oxford Advanced Learner's Dictionary

 

joist

 noun
noun
BrE BrE//dʒɔɪst//
 
; NAmE NAmE//dʒɔɪst//
 
Construction, Structures
 
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a long thick piece of wood or metal that is used to support a floor or ceiling in a building Wordfindercement, construction, foundation, girder, joist, masonry, plaster, rubble, scaffolding, site See related entries: Construction, Structures Word Origin late Middle English giste, from Old French, ‘beam supporting a bridge’, based on Latin jacere ‘lie down’.Extra examples Check that all the floorboards are securely attached to their joists. Lift any loose floorboards and inspect the joists. The ceiling joists must be fire protected. The joists are then nailed into position.
See the Oxford Advanced American Dictionary entry: joist