On the face of it, it's all over (4)

I believe the answer is:

skin

I'm a little stuck... Click here to teach me more about this clue!

'over' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for skin that I've seen before include "Thin outer layer" , "Protective body covering" , "Dermis" , "Surface layer" , "External membrane of body" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.