Adult breaking tenner is loaded? Seriously? (2,7)
I believe the answer is:
in earnest
'seriously?' is the definition.
(synonyms)
'adult breaking tenner is loaded?' is the wordplay.
'adult' becomes 'a' (abbreviation).
'breaking' indicates putting letters inside.
'loaded?' is an anagram indicator (loaded can mean drunk).
'tenner'+'is'='tenneris'
'tenneris' anagrammed gives 'inernest'.
'a' inserted inside 'inernest' is 'IN EARNEST'.
(Other definitions for in earnest that I've seen before include "seriously" , "With serious intentions" , "With serious intention, not fooling about (2.7)" , "with enthusiasm" , "Sincere in intention" .)