Translation guide
The English verb "harden" covers physical stiffening, emotional toughening, and figurative intensification. Japanese uses different verbs depending on what is hardening and whether the change is natural, intentional, or metaphorical.
Describing a substance or object that becomes firm, solid, or rigid, often through cooling, drying, or chemical change.
General intransitive verb for something solidifying or hardening naturally. Used for concrete, jelly, glue, etc.
セメントが固まるまで待ってください。
Please wait until the cement hardens.
ゼリーは冷蔵庫で固まります。
The jelly hardens in the refrigerator.
Transitive verb: to harden something intentionally, like shaping and setting hair, or compacting soil.
ヘアスプレーで髪を固めた。
I hardened my hair with hairspray.
Technical or formal term for hardening, often used in science, engineering, or medical contexts (e.g., resin hardening, arteriosclerosis).
この樹脂は熱で硬化します。
This resin hardens with heat.
Describing a person who becomes less sensitive, more resilient, or emotionally cold, often due to experience.
Literally "turn one's heart into a demon." Means to harden one's heart, usually to do something difficult but necessary.
心を鬼にして、子供を叱った。
I hardened my heart and scolded my child.
To kill one's emotions; to suppress feelings and become emotionally hardened.
彼は感情を殺して淡々と話した。
He hardened his emotions and spoke matter-of-factly.
To become cold-hearted or ruthless. Implies a permanent or severe change in character.
彼は権力を得て冷酷になった。
He hardened after gaining power and became ruthless.
Describing a strengthening of resolve, attitude, or stance, often in the face of opposition.
To firm up one's resolve; to make a firm decision. Very common for personal determination.
彼は留学の決意を固めた。
He hardened his resolve to study abroad.
To harden one's attitude; to take a tougher stance. Often used in negotiations or politics.
政府は交渉での態度を硬化させた。
The government hardened its stance in the negotiations.
To become hawkish or hardline. Used for political or ideological hardening.
党内の意見が強硬になった。
Opinions within the party hardened.
Treating a material to make it harder or more durable, often through industrial processes.
To harden metal by heating and quenching. Standard term in metallurgy.
鋼を焼き入れして硬度を上げる。
Harden the steel by quenching to increase its hardness.
To case-harden; to harden only the surface of a material.
歯車の表面を硬化する処理を施す。
Apply a treatment to harden the surface of the gear.
Direct translations like 「心が固まる」 are not idiomatic and may sound like a physical description. Use set phrases like 「心を鬼にする」 or 「感情を殺す」 instead.
固まる is intransitive (something hardens by itself), while 固める is transitive (someone hardens something). Choose based on whether there is an agent causing the hardening.