Wet fish keeping cool? (5)
I believe the answer is:
rainy
'wet' is the definition.
(similar in meaning)
'fish keeping cool?' is the wordplay.
'fish' becomes 'ray' (ray is a kind of fish).
'keeping' indicates putting letters inside.
'cool?' becomes 'in' ('in' can mean fashionable or cool).
'ray' going around 'in' is 'RAINY'.
(Other definitions for rainy that I've seen before include "Pluvial" , "Save your money for this damp day" , "The day one saves for" , "Wet, showery" , "Drizzly" .)