Mausoleum site shown in indistinct map (7)
I believe the answer is:
diagram
'map' is the definition.
(thesaurus)
'mausoleum site shown in indistinct' is the wordplay.
'mausoleum site' becomes 'agra' (the Taj Mahal is in Agra in India).
'shown in' indicates putting letters inside.
'indistinct' becomes 'dim' (similar in meaning).
'agra' placed within 'dim' is 'DIAGRAM'.
(Other definitions for diagram that I've seen before include "Sketch - plan" , "A grid, Ma? (Anag)" , "Schematic drawing" , "Simplified drawing" , "Drawing or blueprint" .)