Any Japanese learner can use the phrases and expressions in this article starting today. They’re easy to say since they don’t require fancy grammar, and you can use them on their own as interjections or in the beginning of short sentences.
Let’s dive into their meanings, the contexts in which they are used, and example sentences.
了解（りょうかい）
Saying 了解 shows that you not only understand what the other person said but will also comply with their request. The English equivalent is “Roger!” or “Got it!”
You’ll see 了解 a lot when people text each other, but it can be used in formal situations, too.
For instance, when you’re talking with someone in an office, you can either add です or conjugate 了解する to 了解しました.
Example Sentences:
上司と部下の会話 / A Conversation Between A Boss & A Subordinate
A: プレゼンテーションの資料を、来週のミーティングまでに用意してくれますか？
A: Will you please prepare the resources for the presentation by next week’s meeting?
B: 了解です。OR 了解しました。
B: Understood. / Will do.
友達（男性）/ Friends (Men)
A: 来週の金曜日に海に行こうぜ！
A: Let’s go to the ocean next Friday!
B: 了解！カレンダーにいれておくよ。
B: Roger! I’ll put it on my calendar.
友達（女性）/ Friends (Women)
A: ５時半に迎えにきてね。
A: Come to pick me up at half past five, okay?
B: 了解！
B: Got it!
メールで / Via Mail
A: 帰りにスーパーで牛乳買ってきて。
A: Pick up some milk at the supermarket on your way home.
B: 了解！
B: Got it!
もったいない
もったいない means “It’s a waste” or “What a waste!” Simply put, you say もったいない when someone is wasting something they can use. You might hear もったいない when a parent tells their child to not waste food and finish their meal, or when a friend finds out about a missed opportunity. From couples, to friends, to coworkers, anyone can use もったいない.
Example Sentences:
子：ママ、もうお腹いっぱい。これ残していい？
Child: Mom, I’m full already. Can I leave this?
母：もったいない！もう少し食べなさい。
Mother: It’s a waste! Eat a little more.
A: 斉藤君にデートに誘われたけど、断っちゃった。
A: I was asked out on a date by Saitou-kun, but I declined.
B: えー、もったいない！何で？斉藤君、カッコいいのに！
B: Whaaaat? What a waste! Why? Saitou-kun is so cool! (“Even though Saitou-kun is cool…[you turned him down? I can’t believe it!, etc.]”)
A: 読まなかった本を、全部捨てました。
A: I threw away all the books that I didn’t read.
B: もったいない！私が読みたかったです。
B: What a waste! I wanted to read them!
気のせい（きのせい）
気のせい means “It’s just one’s imagination.” If you’re familiar with the grammar pattern 〜せい, you know that it’s used to credit something or someone for a result or consequence. In this case, 気のせい puts the blame on one’s imagination.
Example Sentences:
A: なんか変な音がしない？
A: Do you hear something? (“Isn’t there some strange noise?”)
B: え？何も聞こえないよ。気のせいだよ。
B: Huh? I don’t hear anything. It’s just your imagination.
私、橋本君に嫌われてるのかと思ったけど、気のせいだった。
I thought that I was disliked by Hashimoto-kun, but it was just my imagination.
A: 誰かに見られているような気がする。
A: I feel like I’m being watched by someone.
B: 気のせいだと思うよ。
B: I think it’s just your imagination.
やばい
The original meaning of やばい is “dangerous” or “risky,” and because of that basic meaning, it can be used as an interjection that means “Oh no!” or “Yikes!” But nowadays it can also have a positive connotation in very informal contexts. It’s similar to the word “sick” in English, which literally means “ill,” but can also mean “cool.”
If you’ve run into a difficult situation, like losing your internet connection right when you need it the most, you can shout「やばい！」. Conversely, if you bought a sick new jacket (see the example sentence below), you can also describe it as「やばい！」.
In very informal contexts, you might also hear it as やば or やべー as well (but note that the latter sounds quite coarse, so use it with care).
Example Sentences:
A: 昨日、車ぶつけちゃったよ。
A: Yesterday, I crashed my car.
B: やばい！怪我しなかった？
B: Oh no! Are you okay? (“Were you not injured?”)
A: 明日の試験の準備はどう？
A: How are preparations for tomorrow’s test?
B: やばい！忘れてた！
B: Oh no! I had forgotten about it!
A: それは、やばいね。
A: That’s dicey, isn’t it?
A: 新しいジャケット買ったんだ。みて、これ。やばくない？
A: I bought a new jacket. Look at this. Is this not sick?
B: やばい！すごくカッコいい！
B: Sick! It’s so cool!
A: 昨日の映画はどうだった？
A: How was yesterday’s movie?
B: やばかったね！アクションシーンが本当にすごかった。
B: It was sick, wasn’t it? The action scenes were really incredible.
C: 俳優の演技も、やばかったよね。あの映画、もう一回見たいくらいやばかった！
C: The actor’s acting was wicked too, right? That movie was so sick I want to see it one more time!
気持ち悪い（きもちわるい）
気持ち悪い’s literal meaning is “bad-feeling,” as in something that makes you feel sick to your stomach. But it can also be used to mean something grosses or creeps you out. Whether a spider is crawling near you or you’re watching a horror anime show, this expression comes in handy.
キモい is the shortened version of 気持ち悪い. Unlike 気持ち悪い, キモい can only mean something grosses or creeps you out (not that you literally feel unwell).
You might be wondering why katakana and hiragana characters are combined in the word キモい. This is actually a common occurrence with slang words, and you can learn more about this in this video from the Satori Reader team.
Example Sentences:
気持ち悪い！車酔いしたかも。
I feel sick. I might be carsick.
病院で / At The Hospital
先生：こんにちは。今日はどうされましたか？
Doctor: Hello. What brought you in today (“what happened today”)?
患者：お腹の辺りが気持ち悪くて、少し吐き気もします。
Patient: Around my stomach feels sick, and I have a little bit of nausea.
あの映画のホラーシーン、すごく気持ち悪かったね。
The horror scene from that movie was incredibly creepy, wasn’t it?
知らない人が、私の後をずっとついてきて、すごくキモかった。
A person I didn’t know kept following me, and it was super creepy.
なるほど
なるほど means “I see.” You can use it when you figure something out. For instance, when someone explains how something works to you, reply with なるほど to show that you understood.
However, なるほど doesn’t carry the meaning of compliance like 了解 does. In other words, although なるほど and 了解 both show that you understand what the other person just said, you wouldn’t reply to a request with なるほど. なるほど simply means “I understand what you are saying,” without committing to do anything.
Example Sentences:
A: ここを押すと、ドアが開く。
A: When you press here, the door opens.
B: なるほど！
B: I see!
A: 林君は、引っ越しして家を売ったみたいですよ。
A: It seems that Hayashi-kun moved and sold his house.
B: なるほど、それで彼はあんなに忙しかったんですね。
B: I see, so that’s why he was so busy, huh?
まじ
In casual conversations, Japanese people use まじ when they are shocked or can’t believe what they just heard. It’s like saying “Are you serious?” in English. This makes sense since まじ stems from the word まじめ, which means “serious.”
You can also add で to say まじで, which means “seriously.”
However, since まじ is a slangy term, people often use it without the で, just like we might say “Serious?” in English when we mean “Seriously?”
Example Sentences:
このラーメン、まじでうまいよ。
This ramen is seriously good!
A: 明日からハワイに行くんだ。
A: I’m going to Hawaii from tomorrow.
B: まじ？うらやましいなー。
B: Serious? I’m so jealous!
この映画、まじで面白かったです。
This movie was seriously interesting.
正解（せいかい）
正解 means “the correct answer.” You hear it a lot on Japanese game shows when one of the contestants gets the right answer. You can use 正解 during conversations when someone arrives at the right conclusion or answer as well, as though you were the moderator of a game show.
You can also use 正解 to mean something you did in the past was the right decision (see the last example sentence).
Example Sentences:
A: この問題の答えは、「C」かな？
A: Is the answer to this problem C?
B: 正解！
B: Correct answer! / Bingo!
留学を決めたことは、正解でした。
Deciding on studying abroad was the right decision.
最高（さいこう）
Saying that something is 最高 is like saying “That’s the best” in English. You can even infer the definition just by knowing the meanings of the kanji characters. 最 means “most” while 高 means “high,” so together they mean “the highest; supreme,” or in other words, the best.
Example Sentences:
中森君って、最高だよね！
Nakamori-kun is the best, isn’t he?
昨日のコンサートは最高だったね。
Yesterday’s concert was the best, huh?
今日の天気は最高です。
Today’s weather is supreme.
最低（さいてい）
最低 means “the lowest,” or in other words, “the worst,” so it’s the opposite of 最高. You can tell that 最低 and 最高 are antonyms just from looking at the kanji characters. Both share the character 最, but the second kanji characters, 低 and 高, have opposite meanings, as 低 means “low” while 高 means “high.”
Example Sentences:
この映画は最低だった。
This movie was the worst.
A: 社長が、会社のお金を盗んだらしいです。
A: The company president apparently stole the company’s money.
B: 最低だね！
B: That’s the worst, isn’t it?
パスポートを盗まれて、最低な旅行でした。
I had my passport stolen – it was the worst trip.
Conclusion
Learning how to use short Japanese phrases and expressions like these will help you communicate more naturally because they give you lots of different ways to react to what people say. One of the best ways to make new words and expressions stick is by learning them in an immersive context like in a story. Satori Reader offers dozens of stories written for learners just like you. Click the button below to learn more.