I close home - that's serious (2,7)
I believe the answer is:
in earnest
'serious' is the definition.
(similar in meaning)
'i close home' is the wordplay.
'close' becomes 'near' (similar in meaning).
'home' becomes 'nest' (I've seen this before).
'i'+'near'+'nest'='IN EARNEST'
'that's' acts as a link.
(Other definitions for in earnest that I've seen before include "with sincere intentions" , "seriously" , "Not joking" , "With serious intentions" , "Sincere and serious" .)