Sibling holding in evil (8)
I believe the answer is:
sinister
'evil' is the definition.
(similar in meaning)
'sibling holding in' is the wordplay.
'sibling' becomes 'sister' (I've seen this before).
'holding' is an insertion indicator.
'sister' placed around 'in' is 'SINISTER'.
(Other definitions for sinister that I've seen before include "Threatening; evil-looking" , ", nun going round home" , "Disquieting" , "Suggestive of evil, threatening harm" , "Resist in way that is creepy" .)