/'stɪfn; `stɪfən/
v [I, Ipr, Ip, Tn, Tn.pr, Tn.p] ~ (sth) (up) (with sth) (cause sth to) become stiff or stiffer （使某物）变得（更加）坚硬、僵硬、困难、生硬、强烈等
*My back has stiffened (up) overnight. 我的後背一夜之间强直了.
* He stiffened (with terror) at the horrific sight. 他看到那恐怖的情景吓呆了.
* cotton stiffened with starch 上浆後发挺的棉布
* (fig 比喻) The promise of a reward might stiffen their resolve, ie make them braver. 答应给他们奖励, 他们就可能更勇敢了.

v
[I]
if you stiffen, your body suddenly becomes firm, straight, or still because you feel angry or anxious
≠ relax
　He touched her, and she stiffened.
[I and T]
to become stronger, more severe, or more determined, or to make something do this
　a campaign to stiffen rules against drunk driving
　Their opposition only stiffened my resolve .
[I]alsostiffen up
to become painful and difficult to move
　His joints had stiffened .
　My back had stiffened up.
[T]
to make material stiff so that it will not bend easily