Sorry about the cake (3)
I believe the answer is:
sad
'sorry' is the definition.
(I know that sorry can be written as sad)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for sad that I've seen before include "Dismal" , "Morose" , "Mournful - sorry" , "Tragic" , "Blue" .)