Cul-de-sacs (4,4)
I believe the answer is:
dead ends
'cul-de-sacs' is the definition.
('dead end' can be a synonym of 'cul-de-sac')
This is all the clue.
(Other definitions for dead ends that I've seen before include "they make further progress impossible" , "Saddened in no-progress situations" , "Blind alleys, situations where further progress is impossible" , "Culs de sac?" , "they go nowhere" .)