Live in flat six -- endeavour coming up? (5)
I believe the answer is:
exist
'live' is the definition.
('exist' can be a synonym of 'live')
'in flat six endeavour coming up?' is the wordplay.
'in' indicates a hidden word.
'coming up?' says the letters should be written in reverse.
'tsixe' is hidden in the letters of 'flat six endeavour'.
'tsixe' back-to-front is 'EXIST'.
(Other definitions for exist that I've seen before include "Scrape by" , "Have being or continue living" , "Subsist" , "quick!" , "Live" .)