Genuine nobleman putting King first (4)
I believe the answer is:
real
'genuine' is the definition.
(associated in meaning)
'nobleman putting king first' is the wordplay.
'nobleman putting' becomes 'eal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'king' becomes 'R' (abbreviation of Latin rex).
'first' means one lot of letters go next to another.
'eal' after 'r' is 'REAL'.
(Other definitions for real that I've seen before include "Actual, not imagined" , "Not imaginary, genuine" , "serious" , "Spanish football team" , "Happening in actuality" .)