Definition of knapweed
: any of various weedy centaureas; especially : a widely naturalized European perennial (Centaurea nigra) with tough wiry stems and knobby heads of purple flowers
Origin and Etymology of knapweed
Middle English knopwed, from knop knop + wed weed
First Known Use: 15th century
Seen and Heard
What made you want to look up knapweed? Please tell us where you read or heard it (including the quote, if possible).