“strengthen”

To make stronger or more resistant against attack or weakness.

“Years of adversity had fortified her resolve into something unbreakable.”

Best for: Works well in both physical and emotional contexts; slightly elevated but widely understood.

To support or reinforce something that might otherwise weaken or collapse.

“The new evidence bolstered his argument and silenced the skeptics in the room.”

Best for: Punchy and direct; excellent for journalism, speeches, and persuasive writing.

To reinforce an idea or position by giving it its strongest possible form.

“She steelmanned her opponent's case before dismantling it piece by piece.”

Best for: Modern rhetorical term; ideal for debate, philosophy, and analytical writing.

To strengthen or toughen something through a process of stress or treatment.

“The hardships of the expedition had tempered the crew into a formidable unit.”

Best for: Literary and metaphorical; evokes the imagery of forging metal, lending weight to the prose.

To harden or accustom someone to difficulty until they become resilient.

“Decades at sea had inured him to storms that would terrify lesser sailors.”

Best for: Best for describing gradual toughening through repeated exposure; sophisticated and precise.

To make hard, stubborn, or callously strong through prolonged endurance.

“A life of relentless struggle had indurated his spirit against grief or sentimentality.”

Best for: Rare and archaic-leaning; reserve for literary fiction or highly stylized nonfiction prose.