Slope incorporated railway (7)
I believe the answer is:
incline
'slope' is the definition.
(I know that slope can be written as incline)
'incorporated railway' is the wordplay.
'incorporated' becomes 'inc'.
'railway' becomes 'line' (line is a kind of railway).
'inc'+'line'='INCLINE'
(Other definitions for incline that I've seen before include "Bend forwards" , "Lean (towards)" , "Have a tendency to do or be something" , "Gradient" , "Have tendency or slope" .)