Menacing relative outside home (8)
I believe the answer is:
sinister
'menacing' is the definition.
(I know that menacing can be written as sinister)
'relative outside home' is the wordplay.
'relative' becomes 'sister' (sister is a kind of relative).
'outside' is an insertion indicator (some letters go outside others).
'home' becomes 'in' (to be in is to be (at) home).
'sister' placed around 'in' is 'SINISTER'.
(Other definitions for sinister that I've seen before include "Suggestive of evil, to the left in heraldry" , "Very unpleasant" , "Resist in way that is creepy" , "Disturbing" , "Eerie, alarming" .)