Slippery fish cooked on banks of Tay (6)
I believe the answer is:
shifty
'slippery' is the definition.
(thesaurus)
'fish cooked on banks of tay' is the wordplay.
'cooked' is an anagram indicator (letters cooked into a new form).
'on' means one lot of letters go next to another.
'banks of' suggests removing the centre (the banks are the sides of the word).
'tay' with its centre removed is 'ty'.
'fish' is an anagram of 'shif'.
'shif'+'ty'='SHIFTY'
(Other definitions for shifty that I've seen before include "Suspicious-looking" , "Sneaky and sly" , "Constantly changing; deceitful, evasive" , "Evasive, not straightforward in manner" , "Appearing evasive" .)