mass defect vs mass deficiency

mass defect and mass deficiency both are nouns.

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

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

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

mass defect (noun)	mass deficiency (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