Tough on backside for traveller (7)
I believe the answer is:
pilgrim
'for traveller' is the definition.
(pilgrim is a kind of traveller)
'tough on backside' is the wordplay.
I cannot quite understand how this works, but
'tough' could be 'grim' (I've seen this in another clue) and 'grim' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for pilgrim that I've seen before include "Visitor to shrine" , "Traveller (who made Progress?)" , "Wayfarer to holy site" , "One on journey to shrine" , "Traveller to a sacred place like Mecca" .)