Just five letters and a digit (3)
I believe the answer is:
toe
'digit' is the definition.
(toe is a kind of digit)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for toe that I've seen before include "Pedal extremity" , "One's nailed" , "low digit" , "Pedal digit" , "Lower digit" .)