Destroy pirates (RIP)? No sweat! (12)
I believe the answer is:
perspiration
'sweat' is the definition.
(I know that sweat can be written as perspiration)
'destroy pirates rip? no' is the wordplay.
'destroy' indicates an anagram (I've seen this in other clues).
'pirates'+'rip'+'no'='piratesripno'
'piratesripno' anagrammed gives 'PERSPIRATION'.
(Other definitions for perspiration that I've seen before include "Sweat" , "is exuded" , "Ninety nine percent of genius" .)