Sharp American detectives in charge (6)
I believe the answer is:
acidic
'sharp' is the definition.
(thesaurus)
'american detectives in charge' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'detectives' becomes 'cid'.
'in charge' becomes 'ic'.
'a'+'cid'+'ic'='ACIDIC'
(Other definitions for acidic that I've seen before include "Tart, sour" , "Sharp-tasting, sour" , "Sarcastic or sour" , "Unpleasant" , "Tasting sharp or sour" .)