habitual abortion vs stillbirth

habitual abortion and stillbirth both are nouns.

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

As nouns, stillbirth is a hypernym of habitual abortion; that is, stillbirth is a word with a broader meaning than habitual abortion:

habitual abortion: repeated spontaneous abortion (often for no known reason)
stillbirth: a natural loss of the products of conception

Other hypernyms of habitual abortion include miscarriage, spontaneous abortion.

habitual abortion (noun)	stillbirth (noun)
repeated spontaneous abortion (often for no known reason)	a natural loss of the products of conception