Walk for miles (4)
I believe the answer is:
prom
'walk' is the definition.
(I have seen 'Short walk' mean 'prom' so perhaps 'walk' could also mean 'prom')
'for miles' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'miles' becomes 'm' (common abbreviation).
'pro'+'m'='PROM'
(Other definitions for prom that I've seen before include "hop" , "US high school dance" , "Seaside walk (abbr.)" , "Esplanade" , "Classical music concert for which part of the audience stands" .)