i-adjective
Physical hardness or solidity. 硬い is typical for metal and stone; 固い for firm, solid objects; 堅い for wood and compact materials.
このパンは固くて噛み切れない。
This bread is so hard I can't bite through it.
ダイヤモンドはとても硬い物
Diamond is a very hard substance.
i-adjective
stiff; tight; wooden; unpolished
Lacking flexibility or smoothness. Can describe muscles, joints, writing style, or a formal atmosphere. 堅い is common for stiff writing or formal demeanor.
肩が固くて痛い。
My shoulders are stiff and painful.
彼の文章はまだ堅い感じがする。
His writing still feels stiff and unpolished.
i-adjective
strong; firm; not easily moved
Firm and resistant to pressure or change. Used for resolve, belief, or a substance that holds its shape. 固い is common for firm resolve.
彼は固い決意で試験に臨んだ。
He faced the exam with firm determination.
このゼリーは固くて、スプーンが立つ。
This jelly is so firm that a spoon stands up in it.
i-adjective
steadfast; honest; safe; obstinate
Describes a person's character as reliable and upright, or stubbornly inflexible. 堅い is typical for a trustworthy person; 固い can imply stubbornness. Also used for a safe bet or steady performance.
彼は堅い人で、約束は必ず守る。
He is a steadfast person who always keeps his promises.
あのチームの勝利は固いだろう。
That team's victory seems safe.
父は頭が固くて、新しい考えを受け入れない。
My father is stubborn and won't accept new ideas.
i-adjective
Overly formal, rigid, or lacking casual warmth. Often used for speech, writing, or atmosphere. 堅い is the typical kanji for this sense.
Antonyms: 砕けた
式典の雰囲気はとても堅かった。
The atmosphere at the ceremony was very formal and stiff.
彼の話し方は堅すぎて、親しみにくい。
His way of speaking is too stiff and hard to warm up to.