the.com/joist

means A horizontal beam, usually one of many parallel ones, that supports a floor or ceiling by spanning the gap between walls or supports.

from From Old French 'giste,' meaning a place to lie or rest — itself from the Latin 'iacere,' 'to lie down.' The joist, then, is literally the thing on which something lies: the floorboards rest upon it as a sleeper rests on a bed. The same Latin root branches off into 'gist' (the point on which a matter rests) and even 'gîte,' the French word for a lodging.