ETYMOLOGY
from piss (vb.) + bed (n.),
from its diuretic property;
so French pissenlit (dandelion, bed-wetter)
EXAMPLE
“…Rosecampany; Maudlen, and Cost,
And London touft so red:
Agrimony and Lyons tooth,
That Chyldren call Pysbed…”
From: The Courte of Vertu
By John Hall, 1565
Lexicophilia 