A rest taken on island? That's the way things are (2,2,2)
I believe the answer is:
as it is
'the way things are' is the definition.
(I've seen this before)
'a rest taken on island?' is the wordplay.
'rest' becomes 'sit' (I've seen this in other clues).
'taken on' means one lot of letters go next to another.
'island?' becomes 'is'.
'a'+'sit'+'is'='AS IT IS'
'that's' acts as a link.
(Other definitions for as it is that I've seen before include "Like now" , "Given the position, in the circumstances" , "In current circumstances, the way things are" , "In the existing circumstances" , "true to life" .)