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.
From the word’s history
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."
登入就可以看每一支怎麼連回核心畫面。