Knight accompanying King and master (5)
I believe the answer is:
learn
'master' is the definition.
(I've seen this before)
'knight accompanying king' is the wordplay.
'knight' becomes 'N' (chess abbreviation).
'accompanying' means one lot of letters go next to another.
'king' becomes 'lear' (King Lear).
'n' after 'lear' is 'LEARN'.
'and' acts as a link.
(Other definitions for learn that I've seen before include "Discover - study" , "Acquire knowledge or skill" , "Gain knowledge or skills" , "be taught a lesson" , "Acquire information" .)