Turning it round is laborious (6)
I believe the answer is:
tiring
'laborious' is the definition.
(I've seen this before)
'turning it round' is the wordplay.
'turning' is a reversal indicator.
'round' becomes 'ring' ('ring' can be a synonym of 'round'**).
'it' backwards is 'ti'.
'ti'+'ring'='TIRING'
'is' is the link.
(Other definitions for tiring that I've seen before include "Growing weary or bored" , "Becoming sleepy" , "Exhausting or tedious" , "Laborious" , "Boring" .)