Take the verb cut and add -er, the ending that names the one who does it. What you get is a slot waiting to be filled: the cutter. It can be filled by a thing in your hand, by a person at a bench, or by something that cuts its way through water or air. Notice how the word almost never stands alone. Wire cutters, a pastry cutter, a diamond cutter, a coastguard cutter: a word in front nearly always tells you what is being cut, or where. Meet the word bare and your first job is to look at the words around it.
Wiktionary gives Middle English cutter, cuttere, kutter, and by surface analysis cut + -er.
維基詞典把這個字追到中古英語的 cutter／cuttere／kutter，並指出從字面結構看就是 cut 加上 -er。這條線索直接對上今天的用法：不論指人、指工具還是指船，這個字說的都是「負責切的那一個」。
Wiktionary entry for 'cutter' (packet etymology_text: "From Middle English cutter, cuttere, kutter. By surface analysis, cut + -er.")
Three branches
動手切的人和工具
這一類最貼近核心：真的有東西被切開。-er 有時指工具，有時指人，句子裡兩種都用同一個字，靠上下文分辨。
noun · B1
A tool made for cutting something. The thing it cuts is usually named in front of it, as in wire cutters or a pastry cutter, and tools with two blades are often talked about in the plural.
切割工具
小而快的船
字典只說「小船」，沒有交代這個名字怎麼來的。所以這一支單獨列出來，下面的畫面標明是聯想，不是來源說明。
noun · B2
A small boat or ship. It can be a small sailing boat with one mast, one of the small ships a coastguard uses to patrol the coast, or the small boat a large ship carries for going ashore.
小型船艇
被手指「切」出來的球路
切的動作跑到手指上。手指切過球，球才會往旁邊滑，於是那條球路本身就被叫成 cutter。
noun · C1
In baseball and cricket, a ball thrown or bowled so that it slides sideways instead of coming straight, because the player cut across it with the fingers as it left the hand.
卡特球（切球）