Get away from sides of enormous promontory (6)
I believe the answer is:
escape
'get away from' is the definition.
(thesaurus)
'sides of enormous promontory' is the wordplay.
'sides of' suggests removing the centre (only the letters on the sides remain).
'promontory' becomes 'cape' (I've seen this before).
'enormous' with its middle taken out is 'es'.
'es'+'cape'='ESCAPE'
(Other definitions for escape that I've seen before include "Get free from confinement or control" , "it was great for Steve McQueen!" , "Outlet" , "Get away from confinement" , "Avoid - flight" .)