Obstacle, barrier (6)
I believe the answer is:
hurdle
This clue is a double definition.
'obstacle' is the first definition.
(I know that hurdle is a type of obstacle)
'barrier' is the second definition.
(I know that hurdle is a type of barrier)
(Other definitions for hurdle that I've seen before include "Obstacle to be surmounted" , "Problem to overcome" , "Obstacle; woven fence" , "Obstacle to be jumped over in race" , "Challenge (to be cleared)" .)