Runs fast
(Other definitions for dashes that I've seen before include "Sprints, runs fast" , "Strokes" , "Darts" , "Quick run or sudden rush" , "Makes a quick run" .)
'runs fast' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for gallops that I've seen before include "Runs fast, as a horse say" , "equestrian activities" , "Rides fast" , "Moves quickly" .)