The Spanish interrogative word 'cuál' (meaning 'which' or 'what') comes from the Latin word 'qualis', which meant 'what kind' or 'of what sort'. The evolution from Latin to Spanish shows typical sound changes, where the Latin 'qu-' became 'cu-' in Spanish, and the ending was simplified. This transformation reflects the general pattern of Latin words becoming more streamlined in Spanish.

A related Spanish word is 'cual' (without the accent mark), which is used as a relative pronoun meaning 'which' or 'who'. It's often used in phrases like 'tal cual' (just as) or 'cada cual' (each one). The relationship between 'cuál' and 'cual' shows how the same Latin root developed into both an interrogative and a relative pronoun in Spanish.

While English doesn't have any direct cognates from the Latin 'qualis', we do use related words borrowed from Latin like 'quality' and 'qualify', which share the same root. These words maintain a connection to the original meaning of 'what kind/sort', as 'quality' refers to the nature or characteristics of something, and 'qualify' originally meant to describe or characterize something.