Look closely for a long time at the nobility (7)
I believe the answer is:
peerage
'the nobility' is the definition.
(peerage is a kind of nobility)
'look closely for a long time' is the wordplay.
'look closely' becomes 'peer' (I've seen this before).
'for' says to put letters next to each other.
'a long time' becomes 'age' (an age is a period of time).
'peer'+'age'='PEERAGE'
'at' acts as a link.
(Other definitions for peerage that I've seen before include "Lordly group" , "Book listing lords and the like" , "Group of lords" , "The nobility en masse" , "Dukes, earls, lords, ladies - the lot" .)