Hobo first trudged on slope (5)
I believe the answer is:
tramp
'hobo' is the definition.
(I know that hobo can be written as tramp)
'first trudged on slope' is the wordplay.
'first trudged' becomes 't' (rst letter of 'trudged').
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'slope' becomes 'ramp' (I've seen this before).
't'+'ramp'='TRAMP'
(Other definitions for tramp that I've seen before include "Disreputable wanderer" , "Down-and-out" , "A boat; a vagrant" , "Footslog" , "March heavily like hobo" .)