toughens; toughened; toughening
toughens; toughened; toughening
Learner's definition of TOUGHEN
1
: to make (something) stricter or to become stricter(使)更严厉 [+ object]
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often + up [no object]
—
usually + up 2
: to make (someone) physically or emotionally stronger or to become physically or emotionally stronger(使)更坚强 [+ object]
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often + up [no object]
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usually + up