IV vs digit

IV and digit both are nouns.

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

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

Other hypernyms of IV include figure.

IV (noun)	digit (noun)
administration of nutrients through a vein	a finger or toe in human beings or corresponding body part in other vertebrates
the cardinal number that is the sum of three and one	one of the elements that collectively form a system of numeration
	the length of breadth of a finger used as a linear measure