Use suntan lotion - it helps in the rain (7)
I believe the answer is:
oilskin
'use suntan lotion' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'it helps in the rain' is the wordplay.
I cannot really understand how this works, but
'in' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for oilskin that I've seen before include "protective cloth" , "security for a rainy day" , "Waterproof fabric" , "Waterproof cloth as for sailors" , "Heavy waterproofed cloth" .)