Incan vs Inka

Incan and Inka both are nouns.

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

As nouns, Incan and Inka are synonyms defined as:

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

Other synonyms of Incan include Inca.

Incan (noun)	Inka (noun)
a member of the Quechuan people living in the Cuzco valley in Peru	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

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