Being 'way out' is no longer the thing (4)
I believe the answer is:
exit
'being way out' is the definition.
(I've seen this before)
'no longer the thing' is the wordplay.
'no longer' becomes 'ex' (prefix meaning former or onetime).
'the thing' becomes 'it'.
'ex'+'it'='EXIT'
'is' is the link.
(Other definitions for exit that I've seen before include "Leave the building" , "Way to leave" , "Actor's departure" , "[DOOR] ?" , "Sudden rush of pleasure" .)