Expel some dubious title-holders (4)
I believe the answer is:
oust
'expel' is the definition.
(synonyms)
'some dubious title-holders' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'OUST' can be found hidden inside 'dubious title holders'.
(Other definitions for oust that I've seen before include "Remove and replace" , "Extract" , "Overthrow" , "Drive out, expel" , "Remove from a position or office" .)