1Hard, solid, or tough; firm enough that it does not easily bend, dent, or break (esp. 硬い for metal and stone).
このパンは古くなって硬くなってしまった。
This bread has gone stale and turned hard.
ダイヤモンドは世界で最も硬い物質の一つだ。
Diamond is one of the hardest substances in the world.
肩が硬いので、ストレッチをして体をほぐした。
My shoulders were stiff, so I stretched to loosen up.
固いステーキで、ナイフがなかなか通らなかった。
The steak was so tough that the knife barely cut through it.
2Stiff or wooden; lacking smoothness or naturalness, as in awkward writing, speech, or movement.
緊張のせいか、写真の彼の表情は硬かった。
Perhaps from nerves, his expression in the photo looked stiff.
初めての作文は言い回しが硬くて、読みにくかった。
My first essay had stiff phrasing and was hard to read.
司会の動きが硬くて、会場の空気が和まなかった。
The host's movements were wooden, so the room never warmed up.
3Strong and firm; not easily moved or broken down, as a solid defense or a firm grip.
そのチームは守りが硬く、めったに失点しない。
That team has a solid defense and rarely concedes a point.
彼は最後まで硬い意志を貫いた。
He held firm to his strong will until the very end.
二人の友情は何があっても揺るがない、硬い絆で結ばれている。
The two are bound by a firm friendship that nothing can shake.
4Safe, steady, and reliable; describing a dependable, level-headed person or a sound, low-risk approach.
彼は堅い性格で、約束は必ず守る。
He has a steady character and always keeps his promises.
リスクを取らず、堅い投資先を選んだ。
I avoided risk and chose a safe investment.
あのチームが勝つのはまず堅いだろう。
It's pretty much a safe bet that that team will win.
5Obstinate or stubborn; rigidly unwilling to change one's opinion or attitude.
頭が硬い上司で、新しいやり方を全く受け入れない。
My boss is so hard-headed that he won't accept any new methods at all.
そんなに硬く考えないで、もう少し柔軟になろうよ。
Don't think so rigidly—let's be a bit more flexible.
6Bookish, formal, or stuffy; overly stiff and unapproachable in style or tone (opposite of 砕けた).
この論文は硬い文体で書かれていて、一般の読者には少し難しい。
This paper is written in a bookish style, so it's a bit hard for general readers.
挨拶が硬すぎたので、もう少し砕けた言い方に直した。
The greeting was too formal, so I reworded it more casually.