The Spanish verb 'pesar' comes from the Latin word 'pensare', meaning 'to weigh' or 'to consider'. Over time, while maintaining its original meaning of 'to weigh', the Spanish word evolved to also mean 'to cause regret' or 'to be sorry'. This semantic evolution likely occurred through the metaphorical connection between the weight of physical objects and the emotional weight of regret or sorrow.

Some related Spanish words include the noun form 'el peso' (weight, or the currency), 'pesado' (heavy), and 'pesadumbre' (sorrow, grief). All these words share the core concept of 'weight', either physical or emotional. The currency name 'peso' originally referred to a specific weight of precious metal.

English words related to 'pesar' through the Latin root 'pensare' include 'pensive' (thoughtfully or sadly reflective), 'pension' (originally a payment weighed or considered), and 'compensate' (literally 'to weigh together', meaning to balance or make up for something). The word 'pendant' also comes from this root, as it originally referred to something hanging or weighing down.