It’s extremely common that words do not have direct translations between Japanese and English. Often, this can be because the target language uses more specific words than the source language. Let’s list some interesting examples of this. Are the criteria for what counts super vaguely defined? Perhaps, but let’s do it anyways. Also, my Japanese is garbage (as you can perhaps tell by all these examples being fairly basic words), so let me know if anything looks wrong.
* 足 -> leg, foot
* ダイエット -> diet, exercise (for weight loss)
* ワニ -> alligator, crocodile
* ネズミ -> mouse, rat
* 牛 -> cow, bull
* I -> 俺 (male, casual), 僕 (male, business casual), 私 (kinda formal, or female), わたくし (super formal), あたし (female and outgoing, casual), おいら (male country bumpkin?), 吾輩 (either a pompous talking cat, or perhaps a fire breathing turtle from the Mushroom Kingdom), 俺様(pompous male), etc.
* Good -> 良い (quality, personality, etc.), 美味しい (delicious), 上手 (good at), etc.
* Be (somewhere) -> ある (inanimate), いる (animate)
* Brother -> お兄さん (older brother), 弟さん (younger brother)
* Sister -> お姉さん (older sister), 妹さん (younger sister)
* Water -> 水 (water), お湯 (hot water)
* Better -> （何かより） いい (better), マシ (less bad)
* Run -> 走る(run), 逃げる (run away)
* あの人 -> he, she, (singular) they
* 面白い -> interesting, funny, amusing
* 鍵 -> key, lock
* パンツ -> underwear, pants (though they have different pitch accents, so they’re arguably different words in Japanese too)
* アニメ -> anime, cartoon, animation
* Important -> 大事, 重要 (major, big, critical), 大切 (cherished, valued)
* Job -> 仕事 (generally full-time), アルバイト (part-time)
* Put on (clothes) -> 着る (shirt, coat), 履く (pants, underwear, shoes), かぶる (hat), かける (glasses), する (watch, necklace, gloves), etc.
* （誰かが）好き -> like, love (someone)
* 無理 -> impossible, unreasonable
* 笑う -> smile, laugh
* phone -> 電話 (landline), 携帯 (cellphone)
Feel free to leave more interesting ones below.