nip·ple·wort 
(nĭpəl-wûrt′, -wôrt′)
(nĭpəl-wûrt′, -wôrt′)n.
An annual plant (Lapsana communis) in the composite family, native to Eurasia and naturalized in North America, having small yellow flower heads.
[From its former use in folk medicine to treat breast tumors.]