Ravenously eat up course (4)
I believe the answer is:
flow
'course' is the definition.
(flow is a kind of course)
'ravenously eat up' is the wordplay.
'ravenously eat' becomes 'wolf'.
'up' is a reversal indicator (in down clue: letters go upwards).
'wolf' back-to-front is 'FLOW'.
(Other definitions for flow that I've seen before include "Trickle" , "Well forth" , "Fluid motion" , "Run or move like a liquid" , "(Forward) movement of liquid" .)