Garb for the open air will last longer (7)
I believe the answer is:
outwear
'last longer' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for outwear that I've seen before include "Exhaust" , "Drain" , "Top dressing" , "ride" , "Last longer than others" .)