to make hard or harder

to harden steel.

to make pitiless or unfeeling

to harden one's heart.

to make rigid or unyielding; stiffen

The rigors of poverty hardened his personality.

to strengthen or confirm, esp. with reference to character, intentions, feelings, etc.; reinforce.

to make hardy, robust, or capable of endurance; toughen.

Military . to reinforce the structure of (a military or strategic installation) to protect it from nuclear bombardment.

to become hard or harder.

to become pitiless or unfeeling.

to become rigid or unyielding; stiffen

His personality hardened over the years.

to become confirmed or strengthened

His resistance hardened.

to become inured or toughened

The troops hardened under constant fire.

Commerce . (of a market, prices, etc.)

to cease to fluctuate; firm

When the speculators withdrew from the market, the prices hardened.

to rise higher.

verb

liquefy , melt , soften , be intolerant , indulge , spoil

verb

amalgamate , anneal , bake , brace , buttress , cake , calcify , callous , cement , close , clot , coagulate , compact , congeal , consolidate , contract , crystallize , curdle , densify , dry , firm , fix , fortify , fossilize , freeze , gird , indurate , jell , nerve , ossify , petrify , precipitate , press , reinforce , set , settle , solidify , starch , steel , stiffen , strengthen , temper , thicken , toughen , vitrify , acclimate , acclimatize , adapt , adjust , blunt , brutalize , callus , case-harden , climatize , coarsen , conform , deaden , develop , discipline , dull , embitter , habituate , inure , make callous , numb , paralyze , render insensitive , roughen , season , stun , stupefy , teach , train , concrete , caseharden , accustom , condense , endure , enure , gel , sear