Taste is rancid swallowing a volume (6)
I believe the answer is:
savour
'taste' is the definition.
(synonyms)
'rancid swallowing a volume' is the wordplay.
'rancid' becomes 'sour' (synonyms).
'swallowing' means one lot of letters goes inside another.
'volume' becomes 'v' (abbreviation for volume in book titles).
'a'+'v'='av'
'sour' enclosing 'av' is 'SAVOUR'.
'is' acts as a link.
(Other definitions for savour that I've seen before include "Relish, enjoy" , "Taste or smell something - yummy" , "Delight in" , "Enjoy the flavour" , "Characteristic taste" .)