holy innocents' day: December 28, commemorating Herod's slaughter of the children of Bethlehem
measure: how much there is or how many there are of something that you can quantify
plutonium: a solid silvery grey radioactive transuranic element whose atoms can be split when bombarded with neutrons; found in minute quantities in uranium ores but is usually synthesized in nuclear reactors; 13 isotopes are known with the most important being plutonium 239