octal digit vs digit

octal digit and digit both are nouns.

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

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

Other hypernyms of octal digit include figure.

octal digit (noun)	digit (noun)
a digit from 0 to 7 in octal notation	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