Endless ale drunk entertaining flier (7)
I believe the answer is:
eternal
'endless' is the definition.
(I've seen this before)
'ale drunk entertaining flier' is the wordplay.
'drunk' is an anagram indicator.
'entertaining' indicates putting letters inside (inviting in, as for dinner).
'flier' becomes 'tern' (type of bird).
'ale' with letters rearranged gives 'eal'.
'eal' enclosing 'tern' is 'ETERNAL'.
(Other definitions for eternal that I've seen before include "Without beginning or end" , "Forever and always" , "abiding" , "Immortal" , "going on for ever" .)