Lip, threshold (5)
I believe the answer is:
brink
I believe this is a double definition.
'lip' is the first definition.
(I've seen this in another clue)
'threshold' is the second definition.
(I know that threshold can be written as brink)
(Other definitions for brink that I've seen before include "Verge of an event" , "Threshold" , "Edge of precipice" , "Edge (of disaster etc)" , "Verge (of war etc)" .)