Expression of small distance (5)
I believe the answer is:
smile
'expression' is the definition.
(I know that smile is a type of expression)
'small distance' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'distance' becomes 'mile' (mile is a unit of distance).
's'+'mile'='SMILE'
'of' acts as a link.
(Other definitions for smile that I've seen before include "Friendly facial gesture" , "Pleased expression" , "express pleasure" , "Show happiness" , "Pleasant expression" .)