Area of land is hell — endless weed (7)
I believe the answer is:
hectare
'area of land' is the definition.
(hectare is a unit for measuring land area)
'hell endless weed' is the wordplay.
'hell' becomes 'heck' (interjections!).
'endless' means to remove the last letter.
'weed' becomes 'tare' (I've seen this in another clue).
'heck' with its final letter taken off is 'hec'.
'hec'+'tare'='HECTARE'
'is' is the link.
(Other definitions for hectare that I've seen before include "Ten thousand square metres" , "Extent" , "Metric unit of area" , "Surface area equal to 10,000 square meters" , "The race (anag) - unit of area" .)