Where does “knotweed” come from?

knotweed (English) comes from English knot, from Middle English knotte, from Old English cnotta, from Proto-Germanic knuttô, from Proto-Indo-European gnod- — to bind.

knotweed (English): Any of several plants of the genus "Polygonum",...

Definitions

Any of several plants of the genus "Polygonum",...

Ancestry of “knotweed”, step by step

knotweed traces back through two separate lines of ancestry.

via English knot

Step	Language	Word	Meaning
1	English	knot	A looping of a piece of string or of any other...
2	Middle English	knotte	knot, tie; binding, method of attachment, link;...
3	Old English	cnotta	knot
4	Proto-Germanic	knuttô	a knot
5	Proto-Indo-European	gnod-	to bind

via English weed

Step	Language	Word	Meaning
1	English	weed	Any plant regarded as unwanted at the place...
2	Middle English	weed	—
3	Old English	wēod	weed
4	Proto-West Germanic	*weud	weed (unwanted plant)

Every word from Proto-Indo-European gnod- →Every word from Proto-Germanic knuttô →Every word from Old English cnotta →