I've come across an interesting idiom in the following sentence:

もしも私が社長だったら、あの人を首にすると思います。 If I were the company president, I would fire that person.

What is the origin of the idiom 首にする?

2 Answers 2


I'm an etymology geek -- I love finding out how and when different words and expressions and meanings arose. I offer this as an addition to @sundowner's fine answer post.

What is the origin of the idiom 首にする?

Let's look first at the meanings of 首【くび】. My source is the 日本国語大辞典【にほんこくごだいじてん】 (NKD), basically like the OED only for Japanese. A somewhat abridged version of this dictionary is offered free of charge via the Kotobank resource aggregator website (in Japanese): https://kotobank.jp/

首【くび】 meanings

The NKD entry at Kotobank is here. From that, we learn that 首【くび】 first referred to the "neck", the part of the body along the spine where the torso narrows and connects to the head. This sense is first cited to the 日本書紀【にほんしょき】 of 720, basically around the earliest horizon of any longer texts written in the Japanese language.

Later on, in the late 900s, the word 首【くび】 is cited to mean "the part of the body from the neck upwards", basically synonymous with "head".

Then some 800+ years after that, around 1800, we get a citation of the term used to mean "one's end, specifically with regard to the end of one's relation or connection to someone else", apparently as an extension from the idea of "beheading: losing one's head".

Consider the development of senses for the English word "head", as used in expressions like "it will be your head!" -- we see a similar shift from a literal sense of "the topmost body part", to a reference to losing that body part (and dying), to figurative senses of being fired.

The phrase 首【くび】にする

The NKD entry for this is here. The first citation we see is from 1802, just two years after we see 首【くび】 on its own used to refer to the end of a connection.

The ~にする construction is pretty straightforward: this means "do something into ~, make something into ~, treat something as ~", so the combination of 首【くび】 "one's end" + にする produces the expected meaning of "to bring someone to their end, to end someone, with regard to a relation or connection".


First note that there is another expression (Aの)首を切る, which means the same as (Aを)首にする.

The most relevant expression in English should be head count although I think it is used mostly for hiring. The idea should be just the same, cutting off heads means reducing the number of people.

More precisely, there is a jukugo 馘首{かくしゅ} meaning to fire. According to web searches 馘首 was read くび conventionally, hence 馘首{くび}になる meant to get fired. (I think still になる is sometimes used. Strictly speaking, 首にする/なる is a misusage of 首, albeit totally common.)


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