A bit of liver on fish bone (6)
I believe the answer is:
carpal
'bone' is the definition.
(I've seen this before)
'a bit of liver on fish' is the wordplay.
'bit of' indicates taking the first letters.
'on' means one lot of letters go next to another.
'fish' becomes 'carp' (carp is a kind of fish**).
The initial letter of 'liver' is 'l'.
'a'+'l'='al'
'al' put after 'carp' is 'CARPAL'.
(Other definitions for carpal that I've seen before include "regarding part of the lower arm" , "Wrist bone" , "Of the wrist bones" , "Type of tunnel producing complaint" , "Wrist-bone" .)