One dropping in to see your hand? (6)
I believe the answer is:
caller
This might be a double definition.
'one dropping in to see your' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'hand?' is the second definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for caller that I've seen before include "Someone phoning" , "One paying a brief visit" , "Visitor" , "One visits" , "Person on the line" .)