Invigorate, revitalise (7)
I believe the answer is:
I believe this is a double definition.
'invigorate' is the first definition.
'revitalise' is the second definition.
(Other definitions for freshen that I've seen before include "Re-invigorate" , "(Wind) get stronger" , "(Of wind) become stronger and colder" , "Make less stale" , "Grow stronger (wind)" .)