Old soldier in the posh parts of the Highlands (5)
I believe the answer is:
uhlan
'old' is the definition.
Both the definition and answer are singular nouns.
Maybe they are linked in a way 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 give a lot more credence to this answer).
'parts of' suggests taking the first letters (I've seen 'part' mean this).
The initial letter of 'highlands' is 'h'.
'ulan' going around '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" .)