Powerful? Very! (6)
I believe the answer is:
mighty
This clue is a double definition.
'powerful?' is the first definition.
(I know that powerful can be written as mighty)
'very' is the second definition.
(synonyms)
(Other definitions for mighty that I've seen before include "Strong, powerful" , "Having great strength" , "Large" , "Powerful - exalted" , "Powerful - huge" .)