Garden, it transformed slope (8)
I believe the answer is:
gradient
'slope' is the definition.
(I've seen this before)
'garden it transformed' is the wordplay.
'transformed' indicates an anagram.
'garden'+'it'='gardenit'
'gardenit' anagrammed gives 'GRADIENT'.
(Other definitions for gradient that I've seen before include "Degree of slope in a road" , "Slope or incline" , "Perhaps one in ten" , "Bank" , "Measure of slope" .)