The various meanings of aku (開く, 空く, 悪, 灰汁) with examples

This article will give you all of the knowledge you need on the Japanese word aku, including its various Japanese definitions and translations, example sentences, and more!

What does aku mean?

Aku has a number of different meanings in Japanese, including the verbs to open (開く) and to become vacant (空く), the word for evil (悪), and scum formed when cooking (アク or 灰汁).

Japanese is a sound-poor language with few syllables, so any one “word” (a loose concept here taken to be the same syllables) can take on many different meanings.

In writing, you can usually distinguish which meaning is intended based on the kanji, as you can see in the brackets above.

Let’s take a look at each different usage of aku, together with some examples.

In Japanese, aku has many meanings including "to open", "vacant", "bad", and "scum/foam".

Aku meaning 1: To open

To make it easier for you, I have written each sentence in full Japanese kanji in the first line, followed by roman letters (romaji), and hiragana, with the English meaning coming last.

The first meaning of aku is the verb to open. This is used often in daily conversation and you will write it as 開く.

Mado ga akanai.
The window won’t open.

Chikaku no suupaa wa gozen ku ji ni aku.
The supermarket nearby opens at 9am.

Boku wa doa ga aku no wo matteita.
I waited for the door to open.

I should note in passing that 開く can also be read as hiraku, which also means to open but carries a slightly different connotation (e.g., opening a new business). Let’s leave that one for another day.

Aku meaning 2: To become vacant

Aku can also stand for something being vacant or available. In this case, it is written as 空く. You will often use this when talking about open seats somewhere.

Toshin no kafue de wa aiteiru seki ga nakanaka mitsukaranai.
It’s hard to find any vacant seats in cafes in central Tokyo.

Sumimasen. Koko aiteimasu ka?
Excuse me. Is this seat open? (Lit: Is here open?)

Aku meaning 3: Evil/something bad

In Japanese, aku has many meanings including "to open", "vacant", "bad", and "scum/foam".

In anime and other Japanese entertainment, you might hear aku used to refer to evil. This noun is written as 悪.

Note that 悪 has the same kanji as warui (悪い、わるい), which also means bad but is used as an adjective instead. This adjectival form is a lot more common in conversation.

Aku wa zen no hantai de aru.
Evil is the opposite of good.

Seisho ni wa aku ni tai suru oshie ga ooi.
The Bible also has many teachings on evil.

Aku meaning 4: Scum/foam (in food)

In Japanese, aku has many meanings including "to open", "vacant", "bad", and "scum/foam".

Finally, aku can also stand for the scum or foam that rises to the top of broths, hot pot dishes, and so on. In this case, it is written as 灰汁 or the katakana アク.

This usage may seem a bit obscure, but you will almost certainly encounter アク if you’re a fan of delicious Japanese dishes like nabe and shabushabu!

Aku no tadashii torikata.
How to remove scum correctly

Oishii shabushabu wo taberu ni wa aku wo torinozoku hitsuyou ga arimasu.
If you want your shabushabu to taste good, you need to remove the foam from the top.