Check second highest point (4)
I believe the answer is:
stop
'check' is the definition.
('stop' can be a synonym of 'check')
'second highest point' is the wordplay.
'second' becomes 's' (common abbreviation).
'highest point' becomes 'top' (I've seen this before).
's'+'top'='STOP'
(Other definitions for stop that I've seen before include "Wind up" , "colon, say" , "Pause - prevent" , "Put off for ever" , "Refrain from" .)