spontaneous abortion vs stillbirth

spontaneous abortion and stillbirth both are nouns.

Word	Noun	Adjective	Verb	Adverb
spontaneous abortion	Yes	No	No	No
stillbirth	Yes	No	No	No

As nouns, spontaneous abortion and stillbirth are synonyms defined as:

spontaneous abortion and stillbirth: a natural loss of the products of conception

Other synonyms of spontaneous abortion include miscarriage.

spontaneous abortion (noun)	stillbirth (noun)
a natural loss of the products of conception	a natural loss of the products of conception