Sorry the cake was a failure (3)
I believe the answer is:
sad
'sorry' is the definition.
(I know that sorry can be written as sad)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for sad that I've seen before include "Disconsolate" , "Melancholy or pitiful" , "Effect of winter darkness" , "Regrettable" , "Miserable" .)