Fresh air given to perk up (10)
I believe the answer is:
invigorate
'perk up' is the definition.
(invigorating is a kind of perking up)
'fresh air given to' is the wordplay.
'fresh' is an anagram indicator.
'air'+'given'+'to'='airgivento'
'airgivento' anagrammed gives 'INVIGORATE'.
(Other definitions for invigorate that I've seen before include "Perk up" , "Give strength to" , "Give energy to" , "Liven up" , "Strengthen" .)