To become brown.
Fry the onions until they brown.
To cook something until it becomes brown.
Brown the onions in a large frying pan.
To tan.
Light-skinned people tend to brown when exposed to the sun.
To make brown or dusky.
To give a bright brown colour to, as to gun barrels, by forming a thin coating of oxide on their surface.
(usually derogatory) To turn progressively more Middle Eastern, Hispanic or Latino, in the context of the population of a geographic region.
the browning of America
To treat with deference, or respect.