poppy (n.)

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). Poppy-seed is from early 15c.; in 17c. it also was a small unit of length (less than one-twelfth of an inch).