The Spanish word 'lava' comes from Italian 'lava', which was borrowed from Neapolitan 'lave', meaning 'lava'. The Neapolitan term derives from the Latin verb 'labi', meaning 'to slide' or 'to slip'. This etymology makes intuitive sense, as lava is essentially molten rock that slides or flows down from a volcano. The connection between the Latin word for sliding and the modern term for molten rock likely developed because early observers in the Naples region (home to Mount Vesuvius) needed a way to describe the flowing, sliding nature of volcanic emissions.

The Spanish word 'lavar' (to wash) is related to 'lava', though it comes from a different Latin root ('lavare'). While they're not directly etymologically related, it's a helpful memory aid since both words involve flowing substances - one being molten rock, the other being water for washing.

The English word 'lava' is a direct borrowing of the Italian word, so it's identical to the Spanish word. English also has some words from the Latin root 'labi' (to slide), such as 'lapse' (a slip or fall from a standard) and 'collapse' (to fall or slide down suddenly). These words all share the core concept of sliding or falling movement.