That Scottish G string? (5)
I believe the answer is:
thong
'string?' is the definition.
(a G-string is a type of thong)
'that scottish g' is the wordplay.
'that scottish' becomes 'thon' (Scottish word meaning 'that' or 'that one').
'thon'+'g'='THONG'
(Other definitions for thong that I've seen before include "Strip of leather used for fastening" , "G-string" , "Narrow strip of leather (or other material)" , "Skimpy garment" , "Insubstantial underwear" .)