Poor old mare in noble position (7)
I believe the answer is:
earldom
'noble position' is the definition.
(I've seen this in another clue)
'poor old mare' is the wordplay.
'poor' indicates anagramming the letters.
'old'+'mare'='oldmare'
'oldmare' is an anagram of 'EARLDOM'.
'in' is the link.
(Other definitions for earldom that I've seen before include "Peer's domain" , "noble area of country" , "Aristocratic rank or title" , "Norfolk or Wessex, for example" , "Essex?" .)