1. (

• polonium ,
• Po ,
• atomic_number_ ,

) 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 ;

2. (

• petty_officer ,
• PO ,
• P.O.

) a noncommissioned officer in the Navy or Coast Guard with a rank comparable to sergeant in the Army ;

3. (

• Po ,
• Po_River

) a European river; flows into the Adriatic Sea ;

4. (

• United_States_Post_Office ,
• US_Post_Office ,
• Post_Office ,
• PO

) an independent agency of the federal government responsible for mail delivery (and sometimes telecommunications) between individuals and businesses in the United States ;