tough·en /ˈtʌfən/ (vt.)(vi.)(使)變堅韌,(使)變頑固
Tough·en v. i. & t. [imp. & p. p. Toughened p. pr. & vb. n. Toughening.] To grow or make tough, or tougher. ◄ ►
toughen v : make tough or tougher; "This experience will toughen her"