Bother, the candlestick's covered in grime (10)
I believe the answer is:
disconcert
'bother' is the definition.
(thesaurus)
'the candlestick's covered in grime' is the wordplay.
'the candlestick' becomes 'sconce' (sconce is a kind of candlestick).
'covered in' is an insertion indicator.
'grime' becomes 'dirt' ('dirt' can be a synonym of 'grime').
'sconce' going into 'dirt' is 'DISCONCERT'.
(Other definitions for disconcert that I've seen before include "Bother" , "Throw" , "Dismay" , "Confuse; worry" , "Disturb, unsettle" .)