Allotment next to old address (7)
I believe the answer is:
oration
'address' is the definition.
(oration is a kind of address)
'allotment next to old' is the wordplay.
'allotment' becomes 'ration' (I've seen this in other clues).
'next to' means one lot of letters go next to another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ration' put after 'o' is 'ORATION'.
(Other definitions for oration that I've seen before include "lecture" , "Platform speech" , "Address" , "An eloquent speech" , "Ontario (anag)" .)