The Spanish verb 'dudar' (to doubt) comes from the Latin verb 'dubitare', meaning 'to doubt or hesitate'. 'Dubitare' itself derives from the Latin adjective 'dubius' meaning 'doubtful or uncertain'. Interestingly, 'dubius' comes from the Latin word 'duo' meaning 'two', suggesting that the concept of doubt originally emerged from being of two minds or having to choose between two alternatives.

Some related Spanish words include 'duda' (doubt, noun), 'dudoso' (doubtful), and 'indudable' (undoubtable). These words all share the same Latin root and maintain similar meanings related to uncertainty or questioning.

English speakers might recognize the connection to words like 'doubt', 'dubious', and 'indubitable', which all come from the same Latin root 'dubius'. The word 'dual', meaning relating to two, comes from Latin 'duo', showing another branch of this etymological family. This connection helps illustrate how the concept of 'two-ness' evolved into the notion of uncertainty or hesitation between alternatives.