To move lightly means a lot to a runner (4)
I believe the answer is:
skim
'to move lightly' is the definition.
I can't tell whether this defines the answer.
'a lot to a runner' is the wordplay.
'a lot' becomes 'm'.
'to a' means one lot of letters go next to another (I've seen this in other clues).
'runner' becomes 'ski' (something which 'runs', ie moves quickly on snow).
'm' put after 'ski' is 'SKIM'.
'means' is the link.
Can you help me to learn more?
(Other definitions for skim that I've seen before include "Glide smoothly over" , "copy information illegally" , "Remove top (of milk)" , "avoid paying income tax" , "Brush over" .)