Street sign with an arrow (3-3)
I believe the answer is:
one-way
'street sign with an arrow' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for one-way that I've seen before include "Like non-return valve" , "Street allowing traffic in single direction only" , "This street is single-directional" , "Permitting movement in one direction only" , "Allowing movement in one direction only" .)