The plane designed in East like Jumbo? (11)
I believe the answer is:
elephantine
'like jumbo?' is the definition.
'the plane designed in east' is the wordplay.
'designed' indicates an anagram (designed with the letters).
'east' becomes 'e' ('E' can be a synonym of 'east').
'the'+'plane'='theplane'
'theplane' with letters rearranged gives 'elephant'.
'elephant'+'in'+'e'='ELEPHANTINE'
(Other definitions for elephantine that I've seen before include "Large and bulky" , "Just like Nellie" , "Heavily big" , "Vast" , "Very large or ungainly" .)