Last and worst part (3,3)
I believe the answer is:
fag end
'last and worst part' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for fag end that I've seen before include "Remnant" , "Last piece" , "Butt - something picked up out of context" , "Cigarette butt, the last part" , "Useless bit" .)