Showing your hand to him will reveal your character (12)
I believe the answer is:
graphologist
This might be a double definition.
'showing your hand to him will reveal your' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'character' is the second definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
Can you help me to learn more?
(Another definition for graphologist that I've seen is " Handwriting studier".)