Is it foolish to come out in one? (4)
I believe the answer is:
rash
'one?' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I don't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rash that I've seen before include "Ill-considered - break-out" , "Eruption of spots on skin" , "not considered" , "Flood" , "Impulsive - eruption" .)