nought vs digit

nought and digit both are nouns.

Word	Noun	Adjective	Verb	Adverb
nought	Yes	No	No	No
digit	Yes	No	No	No

As nouns, digit is a hypernym of nought; that is, digit is a word with a broader meaning than nought:

nought: a mathematical element that when added to another number yields the same number
digit: one of the elements that collectively form a system of numeration

Other hypernyms of nought include figure.

nought (noun)	digit (noun)
a mathematical element that when added to another number yields the same number	a finger or toe in human beings or corresponding body part in other vertebrates
	one of the elements that collectively form a system of numeration
	the length of breadth of a finger used as a linear measure