A short dash (6)
I believe the answer is:
hyphen
'a short dash' is the definition.
'a short dash' is the wordplay.
I cannot really understand how this works, but
'short dash' could be 'en' (en dash is a short dash half as long as an em dash) and 'en' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hyphen that I've seen before include "Sign joining words" , "A horizontal word joiner" , "Word-joining mark" , "Line in a double-barrelled name, say" , "Horizontal words joiner" .)