Unusually early to accept it as the truth (7)
I believe the answer is:
reality
'the truth' is the definition.
(thesaurus)
'unusually early to accept it' is the wordplay.
'unusually' indicates anagramming the letters.
'to accept' is an insertion indicator.
'early' with letters rearranged gives 'realy'.
'realy' placed around 'it' is 'REALITY'.
'as' is the link.
(Other definitions for reality that I've seen before include "Truth, actuality" , "Fact" , "The world as it is" , "Type of television" , "All that is actual and not imaginary" .)