Dundee cap (3)
I believe the answer is:
tam
'dundee cap' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tam that I've seen before include "Index rating for TV watching" , "'Scottish cloth cap, in short (3)'" , "Scots cap" , "TV audience ratings" , "Ratings compiled on TV listener numbers" .)