Flit (about) (3)
(Other definitions for dart that I've seen before include "Small narrow pointed missile" , "Sudden quick movement" , "Move quickly and suddenly" , "Small pointed projectile" , "Fish < from River" .)
'flit about' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gad that I've seen before include "country of old" , "biblical tribe" , "wandering about" , "Gallivant in search of pleasure" , "Walk (about)" .)