In Oslo, perhaps, a ramp (5)
I believe the answer is:
slope
'ramp' is the definition.
(I've seen this in another clue)
'in oslo perhaps a' is the wordplay.
'in' says the answer is hidden in the clue.
'SLOPE' is hidden in the letters of 'oslo perhaps a'.
(Other definitions for slope that I've seen before include "Gradient, incline" , "Be inclined" , "Poles for gradient" , "Rake; Barchester chaplain" , "Tilt with poles" .)