Old English court in leading dictionary (abridged version) (4,7)
I believe the answer is:
star chamber
'old english court' is the definition.
(historical English court)
'leading dictionary abridged version' is the wordplay.
'leading' becomes 'star' (synonyms).
'dictionary' becomes 'chambers' (dictionary publisher).
'abridged version' means to remove the last letter.
'chambers' with its last letter removed is 'chamber'.
'star'+'chamber'='STAR CHAMBER'
'in' acts as a link.
(Other definitions for star chamber that I've seen before include "Tyrannical court" , "Court abolished in 1641" , "tribunal" , "Old-fashioned court" , "Old court" .)