Reinvests regularly in very old part of Italy (6)
I believe the answer is:
veneto
'part of italy' is the definition.
(I know that Veneto is part of Italy)
'reinvests regularly in very old' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'in' indicates putting letters inside.
'very' becomes 'v' (common abbreviation).
'old' becomes 'o' (abbreviation).
The alternate letters of 'reinvests' are 'enet'.
'v'+'o'='vo'
'enet' going into 'vo' is 'VENETO'.
(Other definitions for veneto that I've seen before include "Via ..., elegant and expensive Roman street" , "Italian region" , "some Europeans will live here"" , "region of Italy" .)