Fool in Tarsus regularly (3)
I believe the answer is:
ass
'fool' is the definition.
(both can mean a stupid person)
'tarsus regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'tarsus' are 'ASS'.
'in' is the link.
(Other definitions for ass that I've seen before include "Pompous person" , "Braying animal" , "Turkey" , "Long-eared animal" , "Animal related to horses" .)