Large plane required for elephant (5)
I believe the answer is:
jumbo
I believe this is a double definition.
'large plane' is the first definition.
(I've seen this before)
'for elephant' is the second definition.
(I've seen this before)
'required' acts as a link.
(Other definitions for jumbo that I've seen before include "monster" , "Elephant sized?" , "Really big, like an elephant" , "Very large, airliner" , "Elephant - large aircraft" .)