The Spanish word 'ingreso' comes from the Latin word 'ingressus', meaning 'entrance' or 'going in'. This Latin word was formed by combining two elements: the prefix 'in-' meaning 'into, inward' and 'gressus' meaning 'step' or 'walk'. The combination literally meant 'stepping into' or 'walking in', which evolved to mean 'entrance' and later expanded to include the meaning of 'income' in Spanish - conceptually representing money coming in.

Several common Spanish words share the Latin root 'gressus' (step, walk). These include 'progreso' (progress - stepping forward), 'regreso' (return - stepping back), and 'congreso' (congress - stepping together). The prefix 'in-' is also found in many Spanish words like 'incluir' (to include) and 'interior' (interior), always carrying the sense of 'inward' or 'into'.

English speakers can recognize this etymology in words like 'ingress' (entrance), which is a direct cognate of 'ingreso'. The root 'gress' appears in many English words related to walking or stepping, such as 'progress', 'regress', 'congress', and 'aggressive'. The prefix 'in-' is also extremely common in English, appearing in words like 'include', 'inside', and 'input', always indicating inward motion or position.