Returning it with call is wearying (6)
I believe the answer is:
tiring
'is wearying' is the definition.
(synonyms)
'returning it with call' is the wordplay.
'returning' shows that the letters should be reversed in order.
'with' is a charade indicator (letters next to each other).
'call' becomes 'ring' (telephone call).
'it' backwards is 'ti'.
'ti'+'ring'='TIRING'
(Other definitions for tiring that I've seen before include "Boring" , "Causing weariness" , "Exhausting or tedious" , "Growing weary or bored" , "Becoming sleepy" .)