The Spanish word 'opa' meaning 'foolish' comes directly from the Quechua word 'upa', which meant both 'foolish' and 'deaf'. This is one of many words that Spanish borrowed from indigenous South American languages during the colonial period. The slight change from 'upa' to 'opa' reflects Spanish pronunciation patterns.

Since 'opa' entered Spanish directly from Quechua and is already a relatively simple word, there aren't any simpler or more common Spanish words that share its etymology.

There aren't any common English words that are etymologically related to 'opa', as it comes from Quechua, an indigenous South American language family that had no direct contact with English. Any similar-sounding English words would be purely coincidental.