One picture can be held under almost every use of this word: something is pulled tight, or laid out long, and held that way. Strong cloth pulled tight between two becomes a bed you can carry a hurt person on. Canvas pulled tight over four strips of wood becomes a surface a painter can work on, and the wood takes the name. A tool pushed inside a tight shoe pulls the leather wider. A brick laid along the wall shows its long side and runs with the wall. A board fixed across a boat gives the rower's legs something to push against, so the whole body can stretch out into the stroke. Even a lie can be one: the truth pulled further than it really went.
The source entry gives the make-up of the word as stretch + -er, that is, the one that stretches.
來源資料只說明這個字由 stretch（拉開）加 -er（做這件事的人或物）組成，也就是「會把東西撐開的那個」。各個意思怎麼一個一個長出來，這裡是教學上的連結，不是歷史考證。
Wiktionary entry for stretcher (kaikki:3f6f69a190036ae4:844311816:51887): "From stretch + -er."
Four branches
把東西撐開的器具
最貼近字面的一群：stretch 加 -er，就是「會撐開東西的物件」。這一群都是工具，塞進去、繃上去，讓原本緊的東西變鬆、變平。
noun · B2
A person or thing that stretches something, especially a tool made to make something wider or longer — for example a shoe stretcher that you push inside a tight shoe to open it up.
撐開器
繃緊的布：擔架與「被抬走」
把「繃緊的布」抬起來走，就是這一群。布夠緊，人躺上去才不會垮下去——撐開的畫面直接變成一張可以移動的床。
noun · B1
A light bed made of strong cloth pulled tight between two long poles. Two people lift one pole each and carry a person who is lying on the cloth, because that person is too ill or too badly hurt to walk. It is also used to carry a body.
擔架
順著長邊擺的構件
這一群不是被拉開，而是「順著長的方向攤出去」。同樣一塊材料，橫著擺和順著擺名字就不一樣，stretcher 指的是順著走、把長度展開的那一塊。
noun · C1
In building, a brick, stone, or piece of timber that is laid along the length of a wall, so that its long side shows on the face of the wall. A unit turned the other way, with its short end showing, is called a header.
順磚
把話拉過頭
唯一一個離開實物的用法：被拉開的不是布，是一段話。英文也說 stretch the truth，兩個說法共用同一個畫面。
noun · C1
A lie — especially a story that starts from something true and pulls it much further than it really went.
誇大的謊話