Plundering is bad in a servant (7)
I believe the answer is:
pillage
'plundering' is the definition.
('pillage' can be a synonym of 'plundering')
'bad in a servant' is the wordplay.
'bad' becomes 'ill' ('ill' can be similar in meaning to 'bad').
'in' means one lot of letters goes inside another.
'a servant' becomes 'page' (I've seen this before).
'ill' put inside 'page' is 'PILLAGE'.
'is' acts as a link.
(Other definitions for pillage that I've seen before include "Sacking" , "Rob with violence" , "Violent stealing" , "Loot" , "Plunder, sack" .)