Desire Liberal associated with marital consent (6)
I believe the answer is:
libido
'desire' is the definition.
(libido is a kind of desire)
'liberal associated with marital consent' is the wordplay.
'liberal' becomes 'lib'.
'associated with' means one lot of letters go next to another.
'marital consent' becomes 'ido' ('I do' - consent to marriage vows).
'lib'+'ido'='LIBIDO'
(Other definitions for libido that I've seen before include "I'd boil over with sexual energy" , "Sexual drive" , "Sexual impulse" , "Sexual or psychological urge" , "Emotional energy associated with sexual desire" .)