Helmsman's business number (3)

I believe the answer is:

cox

'helmsman's' is the definition.
(cox is a kind of helmsman)

'business number' is the wordplay.
'business' becomes 'co'.
'number' becomes 'x' (X is an example).
'co'+'x'='COX'

(Other definitions for cox that I've seen before include "Passenger vehicle" , "Boat's steerer" , "Helmsman" , "Member of rowing crew" , "Steersman" .)

I've seen this clue in the Evening Standard.

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