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