Be no longer first (5)
I believe the answer is:
exist
'be' is the definition.
(synonyms)
'no longer first' is the wordplay.
'no longer' becomes 'ex' (prefix meaning former or onetime).
'first' becomes 'ist' (ist resembles 1st).
'ex'+'ist'='EXIST'
(Other definitions for exist that I've seen before include "Scrape by" , "Have objective reality" , "Live" , "Be alive" , "Have being or continue living" .)