The Spanish word 'pleural' comes from combining the noun 'pleura' (the membrane that surrounds the lungs) with the adjective suffix '-al'. The noun 'pleura' itself comes from Ancient Greek 'πλευρά' (pleura) which originally meant 'side' or 'rib'. This semantic shift from 'side/rib' to specifically referring to the membrane lining the chest cavity makes sense given the anatomical location of this tissue along the sides of the chest cavity near the ribs.

A simpler related Spanish word is 'pleura', which refers directly to the membrane lining the chest cavity and lungs. While 'pleural' is the adjective form meaning 'relating to the pleura', 'pleura' is the noun form that Spanish learners might encounter first in medical or anatomical contexts.

English speakers might recognize the related word 'pleural' which is identical to the Spanish word and has the same meaning. English also uses 'pleura' as a noun, just like Spanish does. These medical terms were borrowed into both languages ultimately from the same Greek source. You might also encounter these roots in other medical terms like 'pleurisy' (inflammation of the pleura) and 'pleuropneumonia' (inflammation of both the pleura and lungs).