A little yarn to line clothes for the summer ahead (5,5)
I believe the answer is:
short story
'a little yarn' is the definition.
(yarn can mean a story)
'to line clothes for the summer ahead' is the wordplay.
'line' becomes 'ry' (abbreviation for railway).
'clothes for the summer' becomes 'shorts' (shorts are worn in summer).
'ahead' is a charade indicator (letters next to each other) (some letters go in front of others).
'to'+'ry'='tory'
'tory' put after 'shorts' is 'SHORT STORY'.
(Other definitions for short story that I've seen before include "tale" , "little romance, say?" , "not much material to take in" , "Novella" , "That's hardly novel" .)