The Spanish word 'poncho' comes from the Mapudungun (the language of the Mapuche people of Chile and Argentina) word 'pontro', which meant 'woolen cloth'. The Mapuche were skilled in textile production, and this indigenous garment and its name were adopted by Spanish speakers. The meaning evolved slightly from referring to the woolen material itself to specifically meaning the distinctive sleeveless garment worn over the shoulders that we know today.

There aren't any simpler or more common Spanish words that share the same etymology as 'poncho', as it comes directly from an indigenous Mapudungun word rather than from Latin or another major source of Spanish vocabulary.

The English word 'poncho' is borrowed directly from Spanish and has the same meaning. While it might be familiar to English speakers, it's not etymologically related to any native English words since it originated from the indigenous Mapudungun language of South America.