threatened abortion vs imminent abortion

threatened abortion and imminent abortion both are nouns.

Word	Noun	Adjective	Verb	Adverb
threatened abortion	Yes	No	No	No
imminent abortion	Yes	No	No	No

As nouns, threatened abortion and imminent abortion are synonyms defined as:

threatened abortion and imminent abortion: the appearance of symptoms that signal the impending loss of the products of conception

threatened abortion (noun)	imminent abortion (noun)
the appearance of symptoms that signal the impending loss of the products of conception	the appearance of symptoms that signal the impending loss of the products of conception