Help back Scotsman with penny jewel (7)
I believe the answer is:
diamond
'jewel' is the definition.
(I know that diamond is a type of jewel)
'help back scotsman with penny' is the wordplay.
'help' becomes 'aid' (synonyms).
'back' says the letters should be written in reverse.
'scotsman' becomes 'mon'.
'with' is a charade indicator (letters next to each other).
'penny' becomes 'd' (abbreviation e.g. Lsd - pounds, shillings, pence).
'aid' in reverse letter order is 'dia'.
'dia'+'mon'+'d'='DIAMOND'
(Other definitions for diamond that I've seen before include "60th anniversary" , "suited one" , "Form of carbon" , "One of her best friends" , "nickname of US State" .)