Dissipates, chases away (7)
I believe the answer is:
dispels
This clue is a double definition.
'dissipates' is the first definition.
('dispel' can be a synonym of 'dissipate')
'chases away' is the second definition.
('dispel' can be a synonym of 'chase away')
(Other definitions for dispels that I've seen before include "Scatters, drives away" , "'Makes disappear, a doubt say (7)'" .)