'crystal-clear' originates from the word 'crystal,' which comes from the Greek word 'krustallos,' meaning 'ice' or 'rock crystal,' combined with 'clear,' from the Old English 'clǣre,' meaning 'bright' or 'shining.'

'crystal-clear' evolved from the combination of 'crystal' and 'clear' in the English language to describe something that is as clear as a crystal.

Initially, it referred to the literal clarity of a crystal, but over time it evolved to describe anything that is easy to understand or see.