French King having way with Queen in revel (7)
I believe the answer is:
roister
'revel' is the definition.
(roistering is a kind of revelling)
'french king having way with queen' is the wordplay.
'french king' becomes 'roi' (I've seen this before).
'having' means one lot of letters go next to another.
'way' becomes 'st' (**).
'with' says to put letters next to each other.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'roi'+'st'+'er'='ROISTER'
'in' acts as a link.
(Other definitions for roister that I've seen before include "Behave boisterously" , "bluster" , "riot" , "Rioters (anag.)" , "Carouse" .)