Brass instrument player has time for grand household retainer (6)
I believe the answer is:
butler
'retainer' is the definition.
(butler is a kind of retainer)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for butler that I've seen before include "Lofty head servant - what did he see?" , "Valet" , "House servant" , "Senior servant of a household" , "in charge of port?" .)