Always set out for a mountain (7)
I believe the answer is:
everest
'for a mountain' is the definition.
(Mount Everest)
'always set out' is the wordplay.
'always' becomes 'ever' (synonyms).
'out' indicates an anagram (out can mean wrong or inaccurate).
'set' anagrammed gives 'est'.
'ever'+'est'='EVEREST'
(Other definitions for everest that I've seen before include "Tallest mountain ..." , "The world's highest mountain" , "Himalayan mount" , "Highest peak" , "High mountain" .)