To apply water or another liquid to something, especially hair, in order to make it remain lying flat. A noun or pronoun can be used between "wet" and "back." My mom made me wet my hair back for the school photographs.He wetted the decals back with a sticky substance to stop them from peeling up from the side of the car.
wet back
v.
To cause something to lie flat by making it wet and brushing it back: Now that I have short hair, I have to wet it back or it stands on end. I washed my face and wet back my hair.