Number β finger (5)
I believe the answer is:
digit
I believe this is a double definition.
'number' is the first definition.
(digit is a kind of number)
'finger' is the second definition.
(I know that finger can be written as digit)
(Other definitions for digit that I've seen before include "that's on hand" , "One's on hand" , "One in ten, say" , "using 0 or 1 for example" , "Finger, thumb or toe" .)