Cultivation could make it legal (7)
I believe the answer is:
tillage
'cultivation' is the definition.
(I know that cultivation can be written as tillage)
'make it legal' is the wordplay.
'make' indicates an anagram.
'it'+'legal'='itlegal'
'itlegal' is an anagram of 'TILLAGE'.
'could' is the link.
(Other definitions for tillage that I've seen before include "Farming" , "Working of the soil" , "Cultivation of fields" , "digging" , "Farmers undertake it" .)