Suppress, suffocate (6)
I believe the answer is:
stifle
I believe this clue is a double definition.
'suppress' is the first definition.
(I know that stifle is a kind of suppress)
'suffocate' is the second definition.
(I know that suffocate is a kind of stifle)
(Other definitions for stifle that I've seen before include "Repress, choke" , "Part of animal's leg" , "Smother, suffocate" , "Muffle, suppress" , "Repress -- itself (anag)" .)