Strong, potent (8)
I believe the answer is:
powerful
I believe this clue is a double definition.
'strong' is the first definition.
(similar in meaning)
'potent' is the second definition.
(I know that potent can be written as powerful)
(Other definitions for powerful that I've seen before include "Having great strength or influence" , "with lots of horses" , "Having a strong effect" , "Dominant" , "Mighty" .)