The Spanish word 'dueto' (meaning 'duet') comes from the Italian word 'duetto', which was formed by combining the Latin word 'duo' (meaning 'two') with the Italian diminutive suffix '-etto'. This combination literally meant 'little two' or 'small pair', which evolved to specifically refer to a musical performance by two people.

A simpler related Spanish word is 'dos' (meaning 'two'), which also derives from the same Latin root 'duo'. Another related word is 'dúo', which is used similarly to 'dueto' but comes directly from Latin 'duo' without the Italian influence.

Several English words share the same Latin origin 'duo', including 'dual', 'double', and of course 'duo' and 'duet'. The English 'duet' follows the same etymology as Spanish 'dueto', both coming from Italian 'duetto'. This connection makes it easy to remember the Spanish word since it's so similar to its English counterpart.