Congress blocking contribution from members for lack of gravitas (6)
I believe the answer is:
levity
'lack of gravitas' is the definition.
(I've seen this in another clue)
'congress blocking contribution from members' is the wordplay.
'congress' becomes 'it' (congress can mean sex).
'blocking' means one lot of letters goes inside another (block can mean to plug a gap in something).
'contribution from members' becomes 'levy' (I can't justify this - if you can you should give a lot more credence to this answer).
'it' placed within 'levy' is 'LEVITY'.
'for' is the link.
Can you help me to learn more?
(Other definitions for levity that I've seen before include "Light-heartedness" , "Silliness" , "Frivolous tendency" , "Hair-piece" , "Frivolous jocularity" .)