Short line, about a yard and a bit (5)
I believe the answer is:
metre
'short line' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'a yard and a bit' is the wordplay.
'a yard' becomes 'M' (synonyms).
'and' is a charade indicator (letters next to each other).
'a bit' becomes 'etre' (I am not sure about this - if you are sure you should believe this answer much more).
'm'+'etre'='METRE'
'about' is the link.
Can you help me to learn more?
(Other definitions for metre that I've seen before include "Basic unit of length" , "39.37 inches" , "1.094 yards" , "determined by scanning" , "Poetic rhythm" .)