'rub' originates from Middle English, specifically the word 'rubben', of uncertain origin; it may be imitative or connected to older Germanic roots.

'rub' changed from Middle English 'rubben' and eventually became the modern English word 'rub'.

Initially it meant 'to press or move by friction' (a physical action); this core meaning has largely remained in modern usage while extended figurative senses (e.g., 'the rub' = the difficulty) developed later.