harden

/ˈhɑːr.dən/

动词

（使）变硬
The mixture hardens as it cools.
混合物冷却时变硬了。
（使）变严厉，（使）变坚强，（使）变冷酷
Living in the desert hardened the recruits (= made them more strong and determined).
沙漠的艰苦生活把新兵锻炼得更加坚强。