Definitions for knotgrassˈnɒtˌgræs, -ˌgrɑs
Random House Webster's College Dictionary
a common knotweed, Polygonum aviculare, with small leaves and dry fruit that are eaten by birds.
a widespread creeping grass, Paspalum distichum, that forms large mats in shallow waters and ditches.
Origin of knotgrass:
knotgrass, Paspalum distichum(noun)
low-growing weedy grass with spikelets along the leaf stems
An annual plant, Polygonum aviculare, found in fields and wasteland
a common weed with jointed stems (Polygonum aviculare); knotweed
the dog grass. See under Dog