The color red; shades such as crimson or scarlet.
赤いリンゴを一つください。
Please give me one red apple.
彼女は赤いドレスを着てパーティーに来た。
She came to the party wearing a red dress.
夕焼けが空を深い赤に染めた。
The sunset dyed the sky a deep red.
信号の赤は止まれを意味する。
The red traffic light means 'stop'.
A color that contains red (i.e., colors with a reddish tint such as pink, orange, or certain browns).
この絵の具に少し赤を混ぜて暖かい色にしよう。
Add a little red to this paint to make it a warmer color.
秋の葉は緑から赤へと変わる。
Autumn leaves change from green to reddish hues.
そのドレスは赤みのあるオレンジ色だ。
That dress is an orange color with a reddish tint.
Colloquially, a (pejorative) term for communists or people with leftist/communist sympathies; often written as アカ.
彼は学生運動のころアカだと噂されたが、真偽は不明だ。
There were rumors he was a leftist during his student activism days, but it's unclear if they're true.
政治的に敏感な話題なので、誰かを安易に『アカ』と呼ぶのは避けたほうがいい。
Because it's a politically sensitive topic, it's best to avoid casually calling someone 'Aka'.
新聞は彼の過去を引き合いに出して『アカ』だと書いた。
The newspaper cited his past and labeled him 'Aka'.
Abbreviation for a red traffic light (stop signal).
信号が赤だから止まってください。
Stop because the light is red.
交差点で赤を見落として事故になった。
An accident happened when someone missed the red light at the intersection.
Abbreviation referring to red ink (e.g., corrections in red) or to being 'in the red' financially (a deficit).
決算は今年も赤で、会社は対策を検討している。
The financial results are again in the red this year, and the company is considering countermeasures.
先生は答案に赤で直しを書いた。
The teacher marked corrections on the test in red.
Used in compounds or set phrases to mean 'complete' or 'total' (e.g., 赤の他人 — a complete stranger).
あの二人は赤の他人だと聞いた。
I heard those two are complete strangers.
事故の原因は赤裸々に報告された。
The cause of the accident was reported frankly and completely.
Abbreviation for copper (銅, historically called あかがね); an older or dialectal usage referring to copper/bronze.
古い仏具は赤（あか＝銅）でできていたことが多い。
Old Buddhist fittings were often made of copper.
In hanafuda (Japanese playing cards), an abbreviation for the red 5-point card (a scoring card).
花札で赤を揃えて役を作った。
I collected the red cards in hanafuda to make a yaku (hand).