Definition of knotgrass
1
: a cosmopolitan prostrate weed (Polygonum aviculare) of the buckwheat family with jointed stems, prominent sheathing stipules, and minute flowers
broadly
: any of several congeneric plants
2
: any of several grasses (such as Paspalum distichum) with markedly jointed stems
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Merriam-Webster unabridged
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Time Traveler for knotgrass
The first known use of knotgrass was in 1538
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