Strength, potency (5)
I believe the answer is:
power
This clue is a double definition.
'strength' is the first definition.
(I know that power is a type of strength)
'potency' is the second definition.
(synonyms)
(Other definitions for power that I've seen before include "Force - potentiality" , "Ability (to do something)" , "Supremacy, force" , "Strength, force" , "Strength or authority" .)