Number regularly doing Italian (5)
I believe the answer is:
digit
'number' is the definition.
(I know that digit is a type of whole number)
'regularly doing italian' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'italian' becomes 'it' (abbreviation for Italian).
The alternate letters of 'doing' are 'dig'.
'dig'+'it'='DIGIT'
(Other definitions for digit that I've seen before include "Finger; number" , "one's given?" , "Like It?" , "Single numeral" , "Single number" .)