Skirt next to lap (6)
I believe the answer is:
bypass
'skirt' is the definition.
(both can mean to avoid)
'next to lap' is the wordplay.
'next to' becomes 'by'.
'lap' becomes 'pass' (lap can mean to pass in a race).
'by'+'pass'='BYPASS'
(Other definitions for bypass that I've seen before include "Road built to avoid another" , "Road avoiding crowded centres" , "Ring road" , "Secondary channel - kind of operation" , "Road built to avoid a congested area" .)