What does 口 add to words like 出口？

Question

As I am going over the uses of N5 kanji, I have gotten confused as to why 口（ぐち） is used in places such as 出口 and 入口. What meaning does it add?

Answer 1

As you are probably aware, 口 has the meaning of mouth. However, when you look at the Jisho.org definition, you will also find the definition of opening; hole; gap; orifice as well.

What meaning does it add?

In this case, the meaning that is added is pretty simple, opening.

Combining 出 with 口, you get a hole for exiting. You will encounter this at many building and parking lot exits, but it exists many other places as well.

Combining 入 with 口, you get a hole for entering. You will encounter this at many building and parking lot entrances. As with 出口 you will also see it in other places as well.

Answer 2

In 出口 and 入口,「口」describes the doorway.

Answer 3

Here 口 means "doorway" giving

• 入口 "entry" ("entering doorway")
• 出口 "exit" ("exiting doorway")

Of course the principal meaning of 口【くち】 is "mouth" — the opening through which humans or animals take in food. However, besides this literal meaning, "mouth" also has an extended meaning, also in English:

mouth

…

2 An opening or entrance to a hollow, concave, or enclosed structure.

‘the mouth of a cave’

A very similar meaning exists also in Japanese and a monolingual dictionary will list something like the following (taken from 大辞林):

口

…

4. 通り抜けることができる空間。複合語としても用いる（この場合、多く「ぐち」となる）。

   ㋐ 穴やすき間。 「傷－」 「船腹に－があく」

   ㋑ ものを出し入れする所。また、そこをふさぐもの。 「瓶の－」 「 －がかたくて抜けない」

   ㋒ 人の出入りする所。戸口。 「 －が狭い」 「登山－_{とざんぐち}」 「非常－_{ひじようぐち}」

roughly translating to

4. a space where it is possible to pass through; …

   …

   ㋒ where people enter and exit; door or doorway

Note that there are many more such words — the cited dictionary entry gives the following examples:

• 非常口 "emergency exit"
• 登山口 meaning the start of an ascending mountain trail.