Relax, beginning to climb high ground (5)
I believe the answer is:
chill
'relax' is the definition.
(I've seen this before)
'beginning to climb high ground' is the wordplay.
'beginning to' says to take the initial letters.
'high ground' becomes 'hill' (I've seen this before).
The first letter of 'climb' is 'c'.
'c'+'hill'='CHILL'
(Other definitions for chill that I've seen before include "Make cooler" , "Unpleasant coldness in the air" , "This disheartens" , "Feverish cold; relax" , "Cold feeling" .)