Out-of-date sort of chair taken into account (7)
I believe the answer is:
archaic
'out-of-date' is the definition.
(thesaurus)
'sort of chair taken into account' is the wordplay.
'sort of' is an anagram indicator.
'taken into' is an insertion indicator.
'account' becomes 'ac' (abbreviation for account).
'chair' with letters rearranged gives 'rchai'.
'rchai' inserted into 'ac' is 'ARCHAIC'.
(Other definitions for archaic that I've seen before include "Belonging to former times like some words" , "Antiquarian" , "Ancient or out of date" , "Belonging to former times, perhaps word usage" , "A long way out of date" .)