Calculating tool of a coach kept account (6)
I believe the answer is:
'calculating tool' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'a coach kept account' is the wordplay.
'coach' becomes 'bus' (synonyms).
'kept' is an insertion indicator.
'account' becomes 'ac' (abbreviation for account).
'bus' placed around 'ac' is 'bacus'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for abacus that I've seen before include "It will support the architrave" , "An old counting frame with beads" , "As a cub (anag)" , "You could count on this once" , "frame of sorts" .)