For which a damp course is essential (7)
I believe the answer is:
regatta
'for which a damp course is essential' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
Can you help me to learn more?
(Other definitions for regatta that I've seen before include "Series of boat races" , "race on the river" , "Boat race-meeting" , "competition between banks" , "Boat-racing meeting" .)