Very cold, losing free energy (4)
I believe the answer is:
zing
'energy' is the definition.
(I've seen this before)
'very cold losing free' is the wordplay.
'very cold' becomes 'freezing' (freezing means very cold).
'losing' indicates named letters should be taken away.
'freezing' with 'free' removed is 'ZING'.
(Other definitions for zing that I've seen before include "Energy, enthusiasm" , "Energy - liveliness" , "Energy - high-pitched buzz" , "Dynamism" , "Vigour" .)