Three pupils join stern devotee on a journey (7)
I believe the answer is:
pilgrim
'journey' is the definition.
(thesaurus)
'three pupils join stern devotee' is the wordplay.
I cannot quite understand how this works, but
'stern' could be 'grim' (synonyms) and 'grim' is located in the answer.
This explanation may well be incorrect...
'on a' is the link.
Can you help me to learn more?
(Other definitions for pilgrim that I've seen before include "Christian, say" , "Travelling worshipper" , "traveller wanting to visit shrine" , "Visitor to shrine" , "One journeying to holy place" .)