'Bitterweed' definitions:

Widespread European weed with spiny tongue-shaped leaves and yellow flowers; naturalized in United States [syn: oxtongue, bristly oxtongue, bitterweed, bugloss, Picris echioides]

Any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthma [syn: ragweed, ambrosia, bitterweed]