mankind vs humankind

mankind and humankind both are nouns.

Word	Noun	Adjective	Verb	Adverb
mankind	Yes	No	No	No
humankind	Yes	No	No	No

As nouns, mankind and humankind are synonyms defined as:

Other synonyms of mankind include human beings, human race, humanity, humans, man, world.

mankind (noun)	humankind (noun)
all of the living human inhabitants of the earth	all of the living human inhabitants of the earth