The Spanish word 'duda' (meaning 'doubt') has an interesting etymology that traces back to Latin. It originated from the Latin verb 'dubitare' meaning 'to doubt or hesitate', which itself came from the Latin adjective 'dubius' meaning 'doubtful or uncertain'. Interestingly, 'dubius' derives from the Latin word 'duo' meaning 'two', suggesting that doubt originally referred to being of two minds or having to choose between two options. The Spanish noun 'duda' was formed from the verb 'dudar' ('to doubt') with the addition of the feminine noun suffix '-a'.

Some related Spanish words include 'dudar' (the verb 'to doubt'), 'dudoso' (meaning 'doubtful' or 'dubious'), and 'indudable' (meaning 'undoubtable' or 'certain'). All these words share the same Latin root and form a family of words relating to uncertainty and questioning.

English speakers might recognize the connection to words like 'doubt', 'dubious', and 'indubitable', which all come from the same Latin source 'dubitare'. The spelling may be different, but you can hear the similar 'd' sound at the beginning of both 'duda' and 'doubt'. The word 'dual' also comes from Latin 'duo', reflecting the original concept of 'two-ness' that gave rise to the notion of doubt.