Vacuous accountant described by my swearword (4)
I believe the answer is:
oath
'swearword' is the definition.
(oath can mean a swearword)
'vacuous accountant described by my' is the wordplay.
'vacuous' means to remove the middle letters.
'described by' is an insertion indicator (to describe can mean to form an outline).
'my' becomes 'oh' (both are expressions of surprise).
'accountant' with its centre taken out is 'at'.
'at' placed inside 'oh' is 'OATH'.
(Other definitions for oath that I've seen before include "Swearword or solemn promise" , "Vow, sworn word" , "Commitment to tell the truth" , "Profane or obscene expression" , "swearing" .)