poppy (n.)

plant of the genus papaver, having showy flowers and milky juice with narcotic properties, from late Old English popig, popæg, from West Germanic *papua-, probably from Vulgar Latin *papavum, from Latin papaver "poppy," perhaps a reduplicated form of imitative root *pap- "to swell."

Associated with battlefields and war dead at least since Waterloo (1815), an association cemented by John McCrae's World War I poem, they do not typically grow well in the soil of Flanders but were said to have been noticeably abundant on the mass graves of the fallen French after 1815, no doubt nourished by the nutriments below. Poppy-seed is from early 15c.; in 17c. it also was a small unit of length (less than one-twelfth of an inch).