mass deficiency vs mass defect

mass deficiency and mass defect both are nouns.

Word	Noun	Adjective	Verb	Adverb
mass deficiency	Yes	No	No	No
mass defect	Yes	No	No	No

As nouns, mass deficiency and mass defect are synonyms defined as:

mass deficiency and mass defect: the amount by which the mass of an atomic nucleus is less than the sum of the masses of its constituent particles

mass deficiency (noun)	mass defect (noun)
the amount by which the mass of an atomic nucleus is less than the sum of the masses of its constituent particles	the amount by which the mass of an atomic nucleus is less than the sum of the masses of its constituent particles