A number on hand (5)
I believe the answer is:
digit
I believe this clue is a double definition.
'a number' is the first definition.
(digit is a kind of whole number)
'hand' is the second definition.
(I know that hand can be written as digit)
'on' acts as a link.
(Other definitions for digit that I've seen before include "Like It?" , "Finger; numeral" , "a number less than ten" , "A character" , "Single figure - finger" .)