Pô
WordNet
noun
(1) An independent agency of the federal government responsible for mail delivery (and sometimes telecommunications) between individuals and businesses in the United States
(2) A European river; flows into the Adriatic Sea
(3) A noncommissioned officer in the navy with a rank comparable to sergeant in the army
(4) A radioactive metallic element that is similar to tellurium and bismuth; occurs in uranium ores but can be produced by bombarding bismuth with neutrons in a nuclear reactor