An equal in nobility (4)
I believe the answer is:
peer
This clue is a double definition.
'an equal' is the first definition.
(I know that equal can be written as peer)
'nobility' is the second definition.
(peer is a kind of nobility)
'in' is the link.
(Other definitions for peer that I've seen before include "Look closely at equal" , "Look with difficulty; equal" , "Look hard at the nobleman" , "Look searchingly at lord?" , "Noble; look intently" .)