bipolar disorder vs manic depression

bipolar disorder and manic depression both are nouns.

Word	Noun	Adjective	Verb	Adverb
bipolar disorder	Yes	No	No	No
manic depression	Yes	No	No	No

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

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

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

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