Scot's cap (6)
(Other definitions for bonnet that I've seen before include "Baby's hat" , "Type of woman's hat" , "Hat - American hood" , "motor mechanics often raise" , "Old-fashioned woman's hat or a hinged cover over car engine" .)
'scot's cap' 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 "...-o'-shanter, Scottish cap" , "Scots cap" , "'Scottish cloth cap, in short (3)'" , "Scotsman's cap" , "Television ratings system" .)