Large plane required for elephant (5)
I believe the answer is:
jumbo
This clue 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' is the 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" .)