It's easy to get half a mile in front (6)
I believe the answer is:
facile
'it's easy' is the definition.
(synonyms)
'mile in front' is the wordplay.
'mile' becomes 'il' (I can't explain this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'front' becomes 'face' (synonyms).
'il' put within 'face' is 'FACILE'.
'to get half a' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for facile that I've seen before include "Lacking depth, glibly superficial" , "Lacking depth, argument say" , "Easy but glib" , "Smooth" , "Easy or superficial" .)