Boring bit of The Matrix retracted (4)
I believe the answer is:
tame
'boring' is the definition.
(tame can mean dull or boring)
'bit of the matrix retracted' is the wordplay.
'bit of' indicates a hidden word.
'retracted' says the letters should be written backwards.
'emat' is hidden within 'the matrix'.
'emat' reversed gives 'TAME'.
(Other definitions for tame that I've seen before include "Restrained" , "'Domesticated, docile (4)'" , "Flat" , "Not wild, unexciting" , "quiet" .)