Importance causes delay in report (6)
I believe the answer is:
weight
'importance' is the definition.
(weight is a kind of importance)
'delay in report' is the wordplay.
'delay' becomes 'wait' (synonyms).
'in report' shows a homophone (sound like) (ie reportedly, \'we hear\').
'wait' is a homophone of 'WEIGHT'.
'causes' acts as a link.
(Other definitions for weight that I've seen before include "Importance, oppressive force" , "Import" , "Gravitational pull" , "Heavy load - preponderance" , "Vertical force exerted by a mass" .)