Old South American at home with accountant (4)
I believe the answer is:
inca
'old south american' is the definition.
(I've seen this before)
'home with accountant' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'with' means one lot of letters go next to another.
'accountant' becomes 'ca' (abbreviation for chartered accountant).
'in'+'ca'='INCA'
'at' acts as a link.
(Other definitions for inca that I've seen before include "Atahualpa was" , "Pre-conquest South American Indian" , "Early Peruvian" , "member of historic race" , "Inhabitant of old Peru" .)