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Hi ! What's the difference between these words ? In which situations we may use them ?

Thanx !
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As a start: in the botanical world, first a plant wilts (it begins losing water, the drop in pressure decreases its turgidity, and its supporting structures fail to operate; it bends over); second, the plant withers (it begins to dry out, further collapsing; and finally, it shrivels (it curls and wrinkles up as it continues to dry out).

A bit simplistic, but a decent start on using the three words. Your dictionary will supply other meanings.