United approach is never coming back (3-3)
I believe the answer is:
one-way
'never coming back' is the definition.
(a one-way system doesn't let you go backwards)
'united approach' is the wordplay.
'united' becomes 'one' (as in a phrase like 'we are one').
'approach' becomes 'way' (a way of doing something).
'one'+'way'='ONE-WAY'
'is' acts as a link.
(Other definitions for one-way that I've seen before include "Allowing movement in one direction only" , "Kind of street where cars shouldn't meet head-on" , "This street permits traffic only in one entrance and exit (3-3)" , "Street allowing traffic in single direction only" , "Permitting movement in one direction only" .)