1. (noun)polonium, Po, atomic number 84 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 Synonyms: atomic number 84, polonium, pettyofficer
2. (noun)petty officer, PO, P.O. a noncommissioned officer in the Navy or Coast Guard with a rank comparable to sergeant in the Army Synonyms: atomic number 84, polonium, pettyofficer
3. (noun)Po, Po River a European river; flows into the Adriatic Sea Synonyms: atomic number 84, polonium, pettyofficer
4. (noun)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 Synonyms: polonium, atomic number 84, postoffice, localpostoffice, pettyofficer
Synonyms and Antonyms of po 
