Very funny rocks lecturer kept in cupboard (9)
I believe the answer is:
priceless
'very funny' is the definition.
(I've seen this before)
'rocks lecturer kept in cupboard' is the wordplay.
'rocks' becomes 'ice' (as in a drink on the rocks).
'lecturer' becomes 'l' (abbreviation for lecturer).
'kept in' indicates putting letters inside.
'cupboard' becomes 'press' (I've seen this before).
'ice'+'l'='icel'
'icel' inserted inside 'press' is 'PRICELESS'.
(Other definitions for priceless that I've seen before include "Invaluable - very funny" , "Of incalculable value" , "Rich" , "Totally absurd" , "unaffordable?" .)