Villainous group terribly secret seizing power (7)
I believe the answer is:
spectre
'villainous group' is the definition.
(villainous organisation in the James Bond series)
'terribly secret seizing power' is the wordplay.
'terribly' is an anagram indicator.
'seizing' means one lot of letters goes inside another.
'power' becomes 'p'.
'secret' anagrammed gives 'sectre'.
'sectre' going around 'p' is 'SPECTRE'.
(Other definitions for spectre that I've seen before include "something seen as a threat" , "Sceptre (anag.)" , "spirit" , "Narrow ravine" , "after-image?" .)