It could carry an elephant, one imagines (3)
I believe the answer is:
roc
'it could carry an elephant one imagines' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
Can you help me to learn more?
(Other definitions for roc that I've seen before include "Fabulous giant bird of Eastern legend" , "Old bird" , "Gigantic bird of eastern legend - cor!" , "Giant mythical bird" , ".Fabulous bird of the East" .)