The Spanish word 'oreja' (meaning 'ear') comes from the Vulgar Latin 'orecla', which developed from the Latin diminutive form 'auricula' (meaning 'little ear'). 'Auricula' itself was derived from the Latin word 'auris', simply meaning 'ear'. The transformation from 'auricula' to 'oreja' shows typical sound changes that occurred as Latin evolved into Spanish, including the shift from 'au' to 'o' and the palatalization of the 'cl' cluster to 'j'.

A related Spanish word is 'auricular', which refers to something relating to the ear, such as in 'auriculares' (headphones). This word maintains a closer connection to the original Latin form 'auris'.

Several English words share the same Latin root, including 'auricle' (the external part of the ear), 'auricular' (relating to the ear), and 'aural' (relating to the sense of hearing). These English words preserved the original 'aur-' root from Latin 'auris', while Spanish underwent more significant sound changes to arrive at 'oreja'.