Pity it's also rotten (3,3)
I believe the answer is:
too bad
'rotten' is the definition.
(thesaurus)
'pity it's also' is the wordplay.
I cannot really understand how this works, but
'also' could be 'too' (synonyms) and 'too' is found in the answer.
The remaining letters 'bad' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for too bad that I've seen before include "What a pity, hard luck" , "I have no sympathy" , "Informally regrettable - excessively wicked" , "A pity, being excessively naughty" , "That's regrettable, informally" .)