Helpmate's missing sheet - the one that should be on hand
I believe the answer is:
palm
'on hand' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for palm that I've seen before include "Inner surface of the hand" , "Evergreen tree and part of the hand" , "Tree with no branches and large leaves" , "Conceal magician" , "Tree - front of the hand" .)