The Spanish word 'caso' meaning 'case' or 'event' comes from the Latin word 'casus', which meant 'fall' or 'chance, accident'. This Latin noun 'casus' was derived from the verb 'cadere' meaning 'to fall'. The semantic evolution from the concept of 'falling' to 'case/event' can be understood by thinking about how something that 'falls' or 'happens' by chance became associated with circumstances or events in general.

Some related Spanish words include 'caer' (to fall), 'caída' (fall, descent), and 'ocasión' (occasion, opportunity). All these words share the common Latin root related to falling or happening.

English speakers might recognize the connection to words like 'case' (as in a situation or circumstance), 'casual' (happening by chance), and 'occasion' (an event or occurrence). These English words also derive from the same Latin root 'casus', showing how the concept of something 'falling' or 'happening' by chance evolved into words relating to events and circumstances in both languages.