The Spanish word 'equivocado' (meaning 'mistaken') comes from combining the Spanish adjective 'equívoco' ('equivocal, ambiguous') with the past participle suffix '-ado'. Going further back, 'equívoco' derives from the Latin word 'aequivocus' meaning 'ambiguous' or literally 'of equal voice'. The Latin term itself was formed by combining two elements: 'aequus' meaning 'equal' and 'vocare' meaning 'to call'.

The semantic evolution from 'of equal voice' to 'mistaken' makes sense when you consider that something that could be interpreted in multiple equal ways (ambiguous) could lead to mistakes or misunderstandings.

Some related Spanish words include 'equívoco' (ambiguous, equivocal) and the verb 'equivocar(se)' (to make a mistake). These all share the same Latin roots and the core idea of ambiguity or error. The reflexive verb 'equivocarse' is actually more common than the adjective 'equivocado' and means 'to make a mistake' or 'to be mistaken'.

English speakers might recognize the connection to words like 'equivocal' (ambiguous or uncertain) and 'equivocate' (to use ambiguous language to conceal the truth or avoid committing oneself). These English words come from the same Latin roots 'aequus' ('equal') and 'vocare' ('to call'). The 'equal' root 'aequus' is also found in English words like 'equal', 'equation', and 'equator'.