Power, force (5)
I believe the answer is:
might
I believe this clue is a double definition.
'power' is the first definition.
(I know that power can be written as might)
'force' is the second definition.
(might can mean power or force)
(Other definitions for might that I've seen before include "It expresses possibility" , "What functions as an auxiliary" , "Force; could" , "Clout" , "Capability" .)