Savage conserves energy to use as a weapon (5)
I believe the answer is:
wield
'use as a weapon' is the definition.
I can't judge whether this defines the answer.
'savage conserves energy' is the wordplay.
I cannot quite see how this works, but
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is present in the answer.
'savage' could be 'wild' (similar in meaning) and 'wild' is found within the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
'to' is the link.
Can you help me to learn more?
(Other definitions for wield that I've seen before include "Brandish a weapon or exert power" , "exercise" , "Handle - manage" , "Use (weapon, authority)" , "Hold and use (a weapon or tool)" .)