Two at fault regularly arriving at aggregate (5)
I believe the answer is:
total
'aggregate' is the definition.
(I know that aggregate can be written as total)
'two at fault regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'two'+'at'+'fault'='twoatfault'
The alternate letters of 'twoatfault' are 'TOTAL'.
'arriving at' acts as a link.
(Other definitions for total that I've seen before include "final answer" , "Count" , "Final tally" , "Including all" , "Damage beyond repair" .)