'knotweed' originates from Middle English, specifically the word 'knot' meaning 'a node or joint' and 'weed' meaning 'a plant'.

'knotweed' changed from the Middle English word 'knotwede' and eventually became the modern English word 'knotweed'.

Initially, it referred to any plant with jointed stems, but over time it evolved to specifically denote plants in the genus Polygonum.