Start from the verb set: you put something down in the place where it is going to stay, and then you leave it there. Add -er and you have the one that does it. A setter is the one that puts something in position and hands it on — a person who fixes the questions, a player who places the ball, a dog that fixes itself in place, a piece of code that puts a value in. In every case, somebody else moves next.
Wiktionary's entry records setter as coming from Middle English settere, equivalent to set + -er.
本包提供的詞源寫著：setter 來自中古英語 settere，等於 set 加上 -er。這條線索跟現在的用法很合——不管是人、狗還是程式，共同點都是「做 set 這個動作的那一個」。
Wiktionary (kaikki extract) etymology for setter, etymology_number 1: "From Middle English settere, equivalent to set + -er."
Three branches
把規矩、題目訂下來的人
這一組是 set 的抽象用法：定下來的不是一個看得見的東西，而是題目、政策或風格。訂完之後，其他人照著走。
noun · B2
The person who wrote the questions in an exam, a quiz or a crossword puzzle. It is used on its own, often when people are talking about how hard or how clever the questions are.
出題者
把東西擺到定位的那一個
這一組把核心畫面用在看得見的動作上：東西被放到一個好位置，然後交給下一棒。
noun · B1
In volleyball, the player whose job is to take the second touch and lift the ball into a good position so that a teammate can hit it over the net.
舉球員
定住不動的獵犬
這裡 set 的對象是狗自己：牠把自己定在原地。名字記錄的是這個動作，不是狗的長相。
noun · B1
A large dog with long hair, kept and trained to help people hunt. It finds birds or other animals by smell and then stands very still, pointing its body, to show where they are.
雪達犬（長毛獵犬）