Working in the plane, energy is huge (11)
I believe the answer is:
elephantine
'huge' is the definition.
(I've seen this before)
'working in the plane energy' is the wordplay.
'working' indicates an anagram.
'energy' becomes 'e' (physics symbol as in E=mc2).
'in'+'the'+'plane'='intheplane'
'intheplane' is an anagram of 'elephantin'.
'elephantin'+'e'='ELEPHANTINE'
'is' acts as a link.
(Other definitions for elephantine that I've seen before include "Large and clumsy" , "Just like Nellie" , "Ponderously big" , "Jumbo-like" , "Very large or ungainly" .)