Old-fashioned chair in current use (7)
I believe the answer is:
archaic
'old' is the definition.
(similar in meaning)
'fashioned chair in current use' is the wordplay.
'fashioned' indicates anagramming the letters.
'in' indicates putting letters inside.
'current use' becomes 'ac' (I can't justify this - if you can you should believe this answer much more).
'chair' with letters rearranged gives 'rchai'.
'rchai' inserted within 'ac' is 'ARCHAIC'.
Can you help me to learn more?
(Other definitions for archaic that I've seen before include "Belonging to former times, perhaps word usage" , "Antiquated" , "From the past" , "A long way out of date" , "Antiquarian" .)