Fly speck (4)
I believe the answer is:
dash
I believe this is a double definition.
'fly' is the first definition.
(thesaurus)
'speck' is the second definition.
(thesaurus)
(Other definitions for dash that I've seen before include "Fly" , "zip" , "Hyphen; race" , "Short race run at top speed" , "Hurry; hyphen" .)