Inka vs Incan

Inka and Incan both are nouns.

Word	Noun	Adjective	Verb	Adverb
Inka	Yes	No	No	No
Incan	Yes	Yes	No	No

As nouns, Inka and Incan are synonyms defined as:

Inka and Incan: a member of the Quechuan people living in the Cuzco valley in Peru

Other synonyms of Inka include Inca.

Inka (noun)	Incan (noun)
the small group of Quechua living in the Cuzco Valley in Peru who established hegemony over their neighbors in order to create an empire that lasted from about 1100 until the Spanish conquest in the early 1530s	a member of the Quechuan people living in the Cuzco valley in Peru
a member of the Quechuan people living in the Cuzco valley in Peru

Inka (adjective)	Incan (adjective)
	of or pertaining to the Incas or their culture or empire