'Quechuan' originates from Spanish, specifically the word 'quechua', which ultimately comes from the Quechua word 'qichwa' (also spelled 'kichwa'), where 'qichwa' meant 'valley' or 'temperate valley'.

'qichwa' passed into Spanish as 'quechua'; Spanish 'quechua' was adopted into English as 'Quechua', and the adjective form 'Quechuan' developed in English to mean 'of or relating to Quechua'.

Initially it referred to the Quechua people or the Quechua language associated with a particular region ('valley' origin), and over time it has come to be used more broadly in English as both a noun for people and an adjective for anything relating to those peoples or their languages.