rad vs radioactivity unit

rad and radioactivity unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
rad	Yes	No	No	No
radioactivity unit	Yes	No	No	No

As nouns, radioactivity unit is a hypernym of rad; that is, radioactivity unit is a word with a broader meaning than rad:

rad: a unit of absorbed ionizing radiation equal to 100 ergs per gram of irradiated material
radioactivity unit: a measure of radioactivity

rad (noun)	radioactivity unit (noun)
a unit of absorbed ionizing radiation equal to 100 ergs per gram of irradiated material	a measure of radioactivity
the unit of plane angle adopted under the Systeme International d'Unites; equal to the angle at the center of a circle subtended by an arc equal in length to the radius (approximately 57.295 degrees)