Boring master (4)
I believe the answer is:
tame
This clue is a double definition.
'boring' is the first definition.
(tame can mean dull or boring)
'master' is the second definition.
(I've seen this in another clue)
(Other definitions for tame that I've seen before include "quiet" , "Domisticated with meat" , "Flat" , "Restrained" , "far from spicy" .)