bipolar disorder vs manic depressive illness

bipolar disorder and manic depressive illness both are nouns.

Word	Noun	Adjective	Verb	Adverb
bipolar disorder	Yes	No	No	No
manic depressive illness	Yes	No	No	No

As nouns, bipolar disorder and manic depressive illness are synonyms defined as:

bipolar disorder and manic depressive illness: a mental disorder characterized by episodes of mania and depression

Other synonyms of bipolar disorder include manic-depressive psychosis, manic depression.

bipolar disorder (noun)	manic depressive illness (noun)
a mental disorder characterized by episodes of mania and depression	a mental disorder characterized by episodes of mania and depression