Fantastic plane, the jumbo (8)
I believe the answer is:
elephant
'jumbo' is the definition.
(Jumbo was an elephant who lived in London Zoo)
'fantastic plane the' is the wordplay.
'fantastic' is an anagram indicator (a fantastic or improbable ordering of the letters).
'plane'+'the'='planethe'
'planethe' anagrammed gives 'ELEPHANT'.
(Other definitions for elephant that I've seen before include "Trunk carrier?" , "Size of paper" , "it's said to have lots of memory" , "The symbol of the Republican Party" , "Large beast" .)