Pair set out on a long walk (7)
I believe the answer is:
traipse
'a long walk' is the definition.
(I've seen this before)
'pair set out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'pair'+'set'='pairset'
'pairset' anagrammed gives 'TRAIPSE'.
'on' acts as a link.
(Other definitions for traipse that I've seen before include "Walk heavily" , "Trudge around" , "Tedious walk" , "travel wearily" , "Parties (anag.)" .)