Soft stuff that hums terribly (4)
I believe the answer is:
mush
'soft stuff' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'hums terribly' is the wordplay.
'terribly' indicates an anagram.
'hums' anagrammed gives 'MUSH'.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for mush that I've seen before include "mawkishness" , "Schmaltz" , "Go on, Husky!" , "Face" , "Pulpy mass - sloppy sentimentality - command to sled dogs" .)