The Spanish interrogative word 'cuándo' (meaning 'when') comes from the Latin word 'quando', which also meant 'when'. The Latin 'quando' itself was formed from two elements: 'quam' meaning 'how' and a locative particle 'do'. Over time, as Latin evolved into Spanish, 'quando' underwent phonetic changes, with 'qu' becoming 'cu' and the addition of an accent mark to indicate stress, resulting in the modern Spanish 'cuándo'.

Some related Spanish question words that share the same Latin interrogative root 'qu-/cu-' include 'cuál' (which), 'cuánto' (how much), and 'cómo' (how). These words form part of the essential Spanish interrogative vocabulary and follow similar patterns of development from Latin question words.

While English 'when' comes from a different Germanic root, there are some English words that share a distant connection to the Latin 'quando', such as 'quantity' and 'quality', which come from Latin words beginning with the same interrogative element 'qu-'. The word 'quandary', meaning a state of perplexity or doubt, also comes from a Latin source possibly related to 'quando', though its exact etymology is disputed.