Sinister grannie dancing with the lead in Twilight (11)
I believe the answer is:
threatening
'sinister' is the definition.
(I know that sinister can be written as threatening)
'grannie dancing with the lead in twilight' is the wordplay.
'dancing with' indicates anagramming the letters.
'lead in' suggests taking the first letters.
The initial letter of 'twilight' is 't'.
'the'+'t'='thet'
'grannie' mixed up with 'thet' can make 'THREATENING'.
(Other definitions for threatening that I've seen before include "Scary" , "Putting at risk" , "Minatory" , "giving a warning for the future" , "Dangerous" .)