Bit of a grimace from a Scot (3)
I believe the answer is:
mac
'a scot' is the definition.
(many Scottish surnames begin with Mac)
'bit of a grimace from' is the wordplay.
'bit of' indicates a hidden word.
'MAC' is hidden in the letters of 'grimace from'.
(Other definitions for mac that I've seen before include "Waterproof coat (colloq.)" , "laptop?" , "A rainproof" , "one used in shower?" , "It may help you keep dry" .)