Only fish left — chippy's closing (6)
I believe the answer is:
solely
'only' is the definition.
(I know that only can be written as solely)
'fish left chippy's closing' is the wordplay.
'fish' becomes 'sole' (sole is a kind of fish).
'left' becomes 'l' (common abbreviation).
'closing' indicates one should take the final letters (the letter which ends or closes the word).
The last letter of 'chippy' is 'y'.
'sole'+'l'+'y'='SOLELY'
(Other definitions for solely that I've seen before include "nowhere else?" , "Singularly" , "Exclusively, only" , "alone" , "Singly" .)