Scot's hat (3)
I believe the answer is:
tam
'scot's hat' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tam that I've seen before include "Scots hat" , "Ratings compiled on TV listener numbers" , "Index rating for TV watching" , "Scotsman's cap" , "...-o'-shanter, Scottish cap" .)