Seriously close to home on island (2,7)
I believe the answer is:
in earnest
'seriously' is the definition.
(I've seen this before)
'close to home on island' is the wordplay.
'close to' becomes 'near' (I've seen this before).
'home' becomes 'nest' (I've seen this before**).
'on' means one lot of letters go next to another.
'island' becomes 'i'.
'near'+'nest'='nearnest'
'nearnest' after 'i' is 'IN EARNEST'.
(Other definitions for in earnest that I've seen before include "with serious intent" , "Sincere in intention" , "With serious intentions" , "seriously" , "Sincere and serious" .)