'leach' originates from Old English, specifically the word 'lēccan', where the root meant 'to wet or moisten'.

'leach' changed from Old English 'lēccan' (meaning 'to wet, moisten') and through Middle English forms eventually became the modern English word 'leach'; the noun and verb senses developed around the idea of liquid passing through a substance.

Initially, it meant 'to wet or moisten', but over time it evolved into its current technical sense of 'wash out soluble parts by percolation' and the related noun 'leaching' meaning the process.