The Spanish word 'pecho' comes directly from the Latin word 'pectus', meaning 'chest' or 'breast'. This is a straightforward evolution where the Latin '-ctus' ending transformed into '-cho' in Spanish, following common sound changes that occurred as Latin developed into Spanish. The meaning has remained essentially unchanged from Latin to modern Spanish.

Some related Spanish words include 'pechera' (bib or chest protector), 'pechuga' (chicken breast), and 'despechado' (heartbroken, literally 'removed from the chest'). These words all build upon 'pecho' as their root, adding different suffixes to create new meanings related to the chest or breast area.

While English doesn't have many common direct cognates with 'pecho', we do have some technical terms that come from the same Latin root 'pectus'. These include 'pectoral' (relating to the chest or breast), as in 'pectoral muscles' or 'pecs', and 'expectorate' (to cough or spit out, literally 'to expel from the chest'). The medical term 'pectus excavatum' (a congenital deformity of the chest) also preserves the original Latin word.