Business despatches housing assistants
I believe the answer is:
seconds
'assistants' is the definition.
(second is a kind of assistant)
'business despatches housing' is the wordplay.
'business' becomes 'co' (short for company).
'despatches' becomes 'sends' (I've seen this before).
'housing' is an insertion indicator.
'co' going inside 'sends' is 'SECONDS'.
(Other definitions for seconds that I've seen before include "Inferior goods" , "Short periods of time for supporters" , "They should be present at a duel" , "not for long periods?" , "Supports motion" .)