The plane might be a Jumbo (8)
I believe the answer is:
elephant
'a jumbo' is the definition.
(Jumbo was an elephant who lived in London Zoo)
'the plane might be' is the wordplay.
'might be' is an anagram indicator.
'the'+'plane'='theplane'
'theplane' is an anagram of 'ELEPHANT'.
(Other definitions for elephant that I've seen before include "African or Inidan pachyderm" , "Five-toed pachyderm" , "Largest land mammal" , "Source of ivory" , "Jumbo" .)