whiten up

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whiten up

1. To become or appear whiter. His blond hair began whitening up from being in the sunshine all summer long. Try adding a scoop of baking soda to your clothes or linens if you want them to whiten up.
2. To cause something to become or appear whiter. In this usage, a noun or pronoun can be used between "whiten" and "up." The detergent promises to whiten up your clothes. I want to get a toothpaste that whitens up my teeth.
See also: up

whiten up

v.
1. To become whiter: The towels whitened up when I washed them with bleach.
2. To cause something to become whiter: The dentist whitened up my coffee-stained teeth. This polish will whiten your golf shoes up.
See also: up