Slope in field, ending by barn, finally (4)
I believe the answer is:
lean
'slope' is the definition.
(I know that slope is a more specific form of the action lean)
'in field ending by barn finally' is the wordplay.
'in field ending' becomes 'lea' (I can't justify this - if you can you should believe this answer much more).
'by' says to put letters next to each other.
'finally' says to take the final letters.
The last letter of 'barn' is 'n'.
'lea'+'n'='LEAN'
Can you help me to learn more?
(Other definitions for lean that I've seen before include "unremunerative" , "Thin; heel" , "Slant" , "Unprofitable" , "Containing little fat" .)