Naive to have registered leaf (5)
I believe the answer is:
frond
'leaf' is the definition.
(frond is a kind of leaf)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for frond that I've seen before include "part of palm" , "Palm leaf" , "Leaf-like organ" , "Fern leaf" .)