whit ‧ en /ˈwaɪtn/ BrE AmE verb [intransitive and transitive]
[ Word Family: noun : ↑ white , ↑ whiteness , ↑ whitener ; verb : ↑ whiten ; adjective : ↑ white ]
to become more white, or to make something do this:
This stuff is supposed to whiten your teeth.