It is the quechua word in quechua language. In other words, quechua is the castilianization or muteness of kwichua, quichua or better still kwitchua. As language has several rather obvious derivations, the Northern quechua (Colombia and Ecuador), quechua ancashiano or ancashino (Peruvian Central Highlands or Huánuco) and quechua the Southerner in the South of Peru, Bolivia and the Argentine-Chilean North. Usually the word kwichua or quichua, refers more to the southern quechua.
