neckweed
/ˈnɛkwiːd/noun
1 Slang The plant hemp (used with humorous allusion to the use of hempen rope for hanging people).
2 US. Either of two speedwells, Veronica agrestis and V. peregrina, reputed to cure scrofula (tuberculosis of the lymph nodes of the neck). Now rare.
Origin
Mid 16th century; earliest use found in William Bullein (c1515–1576), physician. From neck + weed.