Coarse little devil about to pinch uniform (6)
I believe the answer is:
impure
'coarse' is the definition.
(thesaurus)
'little devil about to pinch uniform' is the wordplay.
'little devil' becomes 'imp' (an imp is a little demon).
'about' becomes 're' ('re' means regarding or about).
'to pinch' indicates putting letters inside.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'imp'+'re'='impre'
'impre' going around 'u' is 'IMPURE'.
(Other definitions for impure that I've seen before include "Adulterated or unchaste" , "Defiled" , "Tainted, not chaste" , "Adulterated, tainted" , "Corrupt" .)