Traveller may be weary, struggling over a great distance (8)
I believe the answer is:
wayfarer
'traveller' is the definition.
(I know that wayfarer is a type of traveller)
'weary struggling over a great distance' is the wordplay.
'struggling' indicates an anagram (the letters struggle or wriggle into a new form).
'over' is an insertion indicator.
'a great distance' becomes 'far' (synonyms).
'weary' anagrammed gives 'wayer'.
'wayer' going around 'far' is 'WAYFARER'.
'may be' acts as a link.
(Other definitions for wayfarer that I've seen before include "Trekker" , "One journeying on foot" , "Foot-traveller" , "Person on a journey - sailing dinghy" , "Traveller, especially on foot" .)