Wearying, exhausting (6)
I believe the answer is:
tiring
I believe this clue is a double definition.
'wearying' is the first definition.
(I know that wearying can be written as tiring)
'exhausting' is the second definition.
(I know that exhausting can be written as tiring)
(Other definitions for tiring that I've seen before include "Becoming sleepy" , "Laborious" , "Wearying, exhausting" , "Causing weariness" , "Boring" .)