Lather (4)
(Other definitions for foam that I've seen before include "Froth, bubbles" , "Bubbles on liquid" , "Boiling bubbles" , "At the mouth, this may mean madness or extreme anger" , "Froth or spume" .)
'lather' is the definition.
(I know that lather can be written as suds)
This is the entire clue.
(Other definitions for suds that I've seen before include "Lather" , "Soap bubbles; scum" , "Soapy water" , "Soapy froth" , "Foam from detergent" .)