Old-fashioned Conservative in a chair, relaxing (7)
I believe the answer is:
archaic
'old-fashioned' is the definition.
(I've seen this before)
'conservative in a chair relaxing' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'in' means one lot of letters goes inside another.
'relaxing' indicates anagramming the letters.
'a'+'chair'='achair'
'achair' anagrammed gives 'arhaic'.
'c' inserted into 'arhaic' is 'ARCHAIC'.
(Other definitions for archaic that I've seen before include "Of a much earlier period" , "Primitive" , "Outdated" , "Belonging to former or ancient times" , "Behind the times" .)