Single-handedly cutting through nonsense? (7)
I believe the answer is:
baloney
'nonsense?' is the definition.
(baloney is a kind of nonsense)
'single-handedly cutting through' is the wordplay.
'single-handedly' becomes 'alone' (I've seen this in another clue).
'cutting' means one lot of letters goes inside another (some letters cut their way into a word).
'through' becomes 'by'.
'alone' inserted into 'by' is 'BALONEY'.
(Other definitions for baloney that I've seen before include "Cobblers" , "Tosh" , "rhubarb" , "deceptive talk" , "foolish talk!" .)