(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) polonium; atomic number 84; po
(a noncommissioned officer in the Navy or Coast Guard with a rank comparable to sergeant in the Army) petty officer; P.O.; po
(a European river; flows into the Adriatic Sea) Po River; po
(an independent agency of the federal government responsible for mail delivery (and sometimes telecommunications) between individuals and businesses in the United States) United States Post Office; US Post Office; Post Office; po