'lean' originates from Old English, specifically the word 'hlēanian' (or similar forms), where the root meant 'to incline or bend'.

'lean' changed from Old English 'hlēanian' into Middle English forms such as 'lenen'/'lĕnen' and eventually became the modern English word 'lean'.

Initially, it meant 'to incline or bend', and over time it kept this core sense while also extending to figurative meanings like 'to have a tendency' or 'to rely on'.