imminent abortion vs threatened abortion

imminent abortion and threatened abortion both are nouns.

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

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

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

imminent abortion (noun)	threatened 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