Read the dictionary definition of po. All definitions for this word.
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 or Coast Guard 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