Revel in a car by the river (7)
I believe the answer is:
carouse
'revel' is the definition.
(carouse is a kind of revel)
'car by the river' is the wordplay.
'by' is a charade indicator (letters next to each other).
'the river' becomes 'ouse' (Yorkshire river).
'car'+'ouse'='CAROUSE'
'in a' acts as a link.
(Other definitions for carouse that I've seen before include "Drink freely and noisily" , "Engage in boisterous, drunken merry-making" , "Celebrate noisily" , "Take a course to party wildly" , "Roister" .)