Advantage of English knight in suit (7)
I believe the answer is:
benefit
'advantage' is the definition.
(I've seen this before)
'english knight in suit' is the wordplay.
'english' becomes 'E' (abbreviation).
'knight' becomes 'n' (chess abbreviation).
'in' indicates putting letters inside.
'suit' becomes 'befit' (synonyms).
'e'+'n'='en'
'en' placed inside 'befit' is 'BENEFIT'.
'of' acts as a link.
(Other definitions for benefit that I've seen before include "Handout" , "Something that aids" , "Advantage (from social security?)" , "Advantage or blessing" , "(Gain) advantage" .)