The Spanish word 'rasta' comes from a shortened form of 'Rastafari', which itself is derived from two Amharic words: 'ras' meaning 'head' or 'governor', and 'tafari' meaning 'one who is to be feared or respected'. These Amharic words were originally combined as a reference to Ras Tafari Makonnen, who later became Emperor Haile Selassie I of Ethiopia, a central figure in the Rastafari movement. The term was adopted into various languages as the movement spread globally, with 'rasta' becoming a common shortened form to refer to followers of Rastafarianism.

There aren't any simpler or more common Spanish words that share the same etymology, as this word was borrowed directly from the Rastafari movement and has Amharic origins rather than Latin or Greek roots that are more common in Spanish vocabulary.

In English, we use similar terms derived from the same source: 'Rasta' and 'Rastafarian'. These words maintain the same meaning as in Spanish, referring to followers of the Rastafari movement or aspects of Rastafari culture. The English terms were borrowed directly from the same Amharic source words 'ras' and 'tafari'.