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A joist is one of the long beams that lie across a building to hold up a floor, or to hold a ceiling from above. When the house is finished you usually cannot see them: they hide under the floorboards or above the ceiling. Builders set many joists side by side, like ribs, then lay the floor on top. They may be wood or steel. Ordinary people often just say beam, and that is close — though actually a joist is a particular kind of beam. It is not the one huge beam that runs the long way through a room. It is one of the many smaller ones that run across, carrying the floor or ceiling. Builders, architects, and people doing repairs use the word. A beam you can see in a barn roof is more often a rafter or just a beam; joists are the hidden floor-and-ceiling ones, unless someone leaves them showing on purpose as a look. There is a rare verb to joist, meaning to fit a floor with joists, but you will almost always meet the noun.
擱柵、托梁
組成From Old French giste, the feminine of gist, the past participle of gesir (“to lie down”) — the beam that lies across.
原始詞典資料2 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
joistnoun/d͡ʒɔɪst/
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A piece of timber or steel laid horizontally, or nearly so, to which the planks of the floor, or the laths or furring strips of a ceiling, are nailed.
- […] a Family was infected there, in so terrible a Manner that every one of the House died; the last Person lay dead on the Floor, and as it is supposed, had laid her self all along to die just before the Fire; the Fire, it seems had fallen from its Place, being of Wood, and had taken hold of the Boards and the Joists they lay on, and burnt as far as just to the Body, but had not taken hold of the dead Body […]
- There are generally forty-two teeth in all; in old whales, much worn down, but undecayed; nor filled after our artificial fashion. The jaw is afterwards sawn into slabs, and piled away like joists for building houses.
joistverb/d͡ʒɔɪst/
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To fit or furnish with joists.
- The floors are joisted with sapling tree trunks, and the flooring itself is made of bark, split and pounded flat into strips. No attempt is made either to fasten or join the strips of flooring.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。