Attendant sick in sack (7)
I believe the answer is:
pillage
'sack' is the definition.
(I've seen this in another clue)
'attendant sick in' is the wordplay.
'attendant' becomes 'page' (page is a kind of attendant).
'sick' becomes 'ill' (similar in meaning).
'in' means one lot of letters goes inside another.
'page' enclosing 'ill' is 'PILLAGE'.
(Other definitions for pillage that I've seen before include "Violent stealing" , "Rob with violence" , "Loot" , "Sacking" , "Plunder, sack" .)