Slip along like a runner with a letter (4)
I believe the answer is:
skim
'slip along' is the definition.
'skim' can be an answer for 'slip' (thesaurus). I am not sure about the 'along' bit.
'a runner with a letter' is the wordplay.
'a runner' becomes 'ski' (something which 'runs', ie moves quickly on snow).
'with' is a charade indicator (letters next to each other).
'a letter' becomes 'm' ().
'ski'+'m'='SKIM'
'like' is the link.
Can you help me to learn more?
(Other definitions for skim that I've seen before include "Remove (or move close to) liquid surface" , "Read cursorily" , "Move quickly (over a surface)" , "Read (something) quickly" , "Remove (cream from milk)" .)