Only entering to be tossed out (8)
I believe the answer is:
obsolete
'out' is the definition.
(I've seen this in another clue)
'only entering to be tossed' is the wordplay.
'only' becomes 'sole' (synonyms).
'entering' is an insertion indicator.
'tossed' indicates anagramming the letters.
'to'+'be'='tobe'
'tobe' with letters rearranged gives 'obte'.
'sole' put inside 'obte' is 'OBSOLETE'.
(Other definitions for obsolete that I've seen before include "Outmoded, passe" , "Boots eel away, being out of date" , "Disused" , "No longer current" , "being out of practice" .)