One missing a book dispatched by European conglomerate, finally (8)
I believe the answer is:
absentee
'one missing' is the definition.
(someone who is absent)
'a book dispatched by european conglomerate finally' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'dispatched' becomes 'sent' (I've seen this before).
'by european' becomes 'e' (abbreviation e.g. EU. I am not sure about the 'by' bit.).
'finally' indicates one should take the final letters.
The last letter of 'conglomerate' is 'e'.
'a'+'b'+'sent'+'e'+'e'='ABSENTEE'
(Other definitions for absentee that I've seen before include "One failing to attend" , "He's not here!" , "Missing person" , "One away from work, etc" , "one's failed to show up" .)