Weapon that somehow combines power and lots of energy (4)
I believe the answer is:
epee
'weapon' is the definition.
(epee is a kind of weapon)
'somehow combines power and lots of energy' is the wordplay.
I cannot really see how this works, but
'power' could be 'pe' (P.E. is an example) and 'pe' is found within the answer.
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is present in the answer.
A single letter 'e' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
'that' is the link.
(Other definitions for epee that I've seen before include "there's a point to it" , "Sharp-pointed duelling sword" , "Duelling blade" , "Fencing sword, heavier than a foil" , "Use it to fence" .)