Noble rank open to knight: earl (7)
I believe the answer is:
grandee
'noble' is the definition.
(grandee is a kind of noble)
'rank open to knight earl' is the wordplay.
'rank' becomes 'grade' (synonyms).
'open to' is an insertion indicator.
'knight' becomes 'N' (chess abbreviation).
'earl' becomes 'e'.
'grade' going around 'n' is 'grande'.
'grande'+'e'='GRANDEE'
(Other definitions for grandee that I've seen before include "Enraged (anag) - Spanish nobleman" , "Eminent person" , "Person of high rank" , "Person of eminence" , "Eminent man" .)