Old soldier in the posh parts of the Highlands (5)
I believe the answer is:
uhlan
'old' is the definition.
Both the answer and definition are singular nouns.
Maybe there's an association between them I don't understand?
'in the posh parts of the highlands' is the wordplay.
'in the' is an insertion indicator.
'posh' becomes 'ulan' (I can't justify this - if you can you should believe this answer much more).
'parts of' suggests taking the first letters (I've seen 'part' mean this).
The first letter of 'highlands' is 'h'.
'ulan' enclosing 'h' is 'UHLAN'.
'soldier' is the link.
Can you help me to learn more?
(Other definitions for uhlan that I've seen before include "Prussian lancer" , "Horseman once" , "Cavalryman" .)