Shower curtain not cut (4)
I believe the answer is:
rain
'shower' is the definition.
(rainfall)
'curtain not cut' is the wordplay.
'not' indicates named letters should be taken away.
'curtain' with 'cut' taken out is 'RAIN'.
(Other definitions for rain that I've seen before include "See 12" , "bad weather" , "Precipitation" , "The right" , "Weather - shower" .)