Terrible fish rising (3)
I believe the answer is:
bad
'terrible' is the definition.
(similar in meaning)
'fish rising' is the wordplay.
'fish' becomes 'dab' (dab is a type of fish).
'rising' says the letters should be written backwards (going up in a down clue).
'dab' reversed gives 'BAD'.
(Other definitions for bad that I've seen before include "Harmful" , "Ill" , "Wicked" , "Evil, below standard or off" , "(Of food) decayed" .)