No longer active, one-time Conservative's put in shade (7)
I believe the answer is:
extinct
'no longer active' is the definition.
(as in an extinct volcano)
'one-time conservative's put in shade' is the wordplay.
'one-time' becomes 'ex' (prefix meaning former or onetime).
'conservative' becomes 'C' (UK political abbreviation).
'put in' is an insertion indicator.
'shade' becomes 'tint' (synonyms).
'c' placed within 'tint' is 'tinct'.
'ex'+'tinct'='EXTINCT'
(Other definitions for extinct that I've seen before include "No longer around" , "Having died out, animal species or volcano" , "Like a dodo" , "Having died out, like the dinosaur" , "Of volcano, no longer active" .)