Skin ulcerated badly with soft soap (7)
I believe the answer is:
treacle
'skin ulcerated badly with soft soap' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
This is all the clue.
Can you help me to learn more?
(Other definitions for treacle that I've seen before include "Syrup, molasses" , "Carroll's sisters had to live with" , "well described by Dormouse" , "Contrived sentimentality - sticky substance" , "Thick, sticky, dark syrup" .)