One rebuilt chair in a hundred is antique (7)
I believe the answer is:
archaic
'is antique' is the definition.
(thesaurus)
'one rebuilt chair in a hundred' is the wordplay.
'one rebuilt' indicates anagramming the letters.
'in' indicates putting letters inside.
'hundred' becomes 'c' (Roman numeral).
'chair' anagrammed gives 'rchai'.
'a'+'c'='ac'
'rchai' put inside 'ac' is 'ARCHAIC'.
(Other definitions for archaic that I've seen before include "Ancient, no longer current" , "Very old or old-fashioned" , "Primitive" , "From the past" , "Antiquated" .)