1 [I,T] to become or to make sth hard or less likely to change （使）变硬或强硬: The concrete will harden in 24 hours. 混凝土可于24小时内凝固。The firm has hardened its attitude on this question. 公司对这个问题的态度变得强硬了。

2 [T] (usually passive 通常用于被动语态) harden sb (to sth/doing sth) to make sb less kind or less easily shocked 使心肠变硬；使见怪不怪: a hardened reporter/criminal 铁石心肠的记者／罪犯Police officers get hardened to seeing dead bodies. 警察看见尸体已经习以为常了。

3 [I] (used about a person's face, voice, etc) to become serious and unfriendly （指人的脸色、说话声音等）变得严峻