0 to become or make hard: --
1 to become more severe, determined, or unpleasant: --
As the war progressed, attitudes on both sides hardened (= became more severe and determined).
Living in the desert hardened the recruits (= made them more strong and determined).
3 to become firm or solid, or to cause something to become firm or solid: --
Meanwhile, the soil may be drying, hardening, crusting and heating up.
Alternatively, people hardened by war or personal crisis can at times appear 'numbed' or in shock.
All plants were hardened off outdoors in direct sunlight 24 h prior to use.
Initially it is rather soft, moist and fibrous, but it hardens and dries out with time.
After ecdysis the pupa was pale greenish, but it rapidly hardened and darkened to brown with traces of green coloration under the wings.
During their earthly lives it is hardened in error.
With the application of ultraviolet light, the epoxy cures to its fully hardened state with no mixing or additional mess.
Low-temperature plastic deformation of the veins, without significant recovery, will also result in work hardening leading ultimately to fracture.
