A large object in parliament (7)
I believe the answer is:
althing
'parliament' is the definition.
(Icelandic parliament)
'a large object' is the wordplay.
'large' becomes 'l'.
'object' becomes 'thing' (thing is a kind of object**).
'a'+'l'+'thing'='ALTHING'
'in' acts as a link.
(Other definitions for althing that I've seen before include "Icelandic parliament" , "Island parliament" .)