European working a very long time (3)
I believe the answer is:
eon
'a very long time' is the definition.
(I've seen this before)
'european working' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'working' becomes 'on'.
'e'+'on'='EON'
(Other definitions for eon that I've seen before include "An immense time" , "Geological period" , "Major division of geological time" , "billion years" , "Age, epoch" .)