A novel bit of rash expenditure (3)
I believe the answer is:
she
'a novel' is the definition.
(I've seen this before)
'bit of rash expenditure' is the wordplay.
'bit of' indicates a hidden word.
'SHE' can be found hidden inside 'rash expenditure'.
(Other definitions for she that I've seen before include "Book" , "way to refer to mare" , "H. Rider Haggard novel" , "lady" , "Female pronoun" .)