Always set out for the highest mountain (7)
I believe the answer is:
everest
'the highest mountain' is the definition.
(I've seen this before)
'always set out' is the wordplay.
'always' becomes 'ever' (synonyms).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'set' anagrammed gives 'est'.
'ever'+'est'='EVEREST'
'for' acts as a link.
(Other definitions for everest that I've seen before include "Great achievement" , "Where Hillary was" , "The world's highest mountain" , "Tallest mountain ..." , "Highest Himalayan mountain" .)