Spirit embodied by secular Magna Carta (8)
I believe the answer is:
armagnac
'spirit' is the definition.
(I've seen this before)
'embodied by secular magna carta' is the wordplay.
'embodied by' says the answer is hidden in the clue.
'ARMAGNAC' is hidden within 'secular magna carta'.
(Other definitions for armagnac that I've seen before include "A gram can for a French brandy" , "stronger drink than ale" , "Brandy traditionally made in Aquitaine" , "Kind of brandy" , "Liquor" .)