What is the verb for thin?

Answer 1

Thin is already a verb when used in the right context. As in "to thin something".
Thins, thinning and thinned are also verbs.

Some example sentences are:
"We need to thin down the soup".
"She thins the trimmings".
"The gravy needs thinning down".
"The sauce has been thinned too much".

Answer 2

The verb for "thin" is "to thin."

Answer 3

I thinned down this summer.