One female relation and one companion being inert (9)
I believe the answer is:
inanimate
'inert' is the definition.
(thesaurus)
'one female relation and one companion' is the wordplay.
'one' becomes 'i' (Roman numeral).
'female relation' becomes 'nan' (grandmother).
'and' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'companion' becomes 'mate' (both can mean a friend).
'i'+'nan'+'i'+'mate'='INANIMATE'
'being' acts as a link.
(Other definitions for inanimate that I've seen before include "dead" , "Not endowed with life" , "Lifeless, showing no signs of activity" , "Without life" , "Not alive" .)