But this Scottish area is not in the Tweed! (6)
I believe the answer is:
harris
'tweed' is the definition.
(Harris tweed is an example)
'but this scottish area is not' is the wordplay.
I cannot quite see how this works, but
'area' could be 'a' (maths abbreviation) and 'a' is present in the answer.
'is' is present in the answer.
This explanation may well be incorrect...
'in the' acts as a link.
Can you help me to learn more?
(Other definitions for harris that I've seen before include "Hebridean area associated with tweed" , "Isle known for tweed" , "Hebridean area known for tweed" , "location off Scottish mainland" , "Lewis with ------, Hebridean island" .)