Shaving lather (4)
I believe the answer is:
foam
'shaving lather' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for foam that I've seen before include "Sea froth" , "Froth, bubbles" , "Lather, froth" , "Suspension of gas in a liquid" , "Froth or spume" .)