名詞 p.o.:

1. a noncommissioned officer in the navy with a rank comparable to sergeant in the army
   同義詞：petty officer, PO
2. 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
   同義詞：polonium, Po, atomic number 84
3. a European river; flows into the Adriatic Sea
   同義詞：Po, Po River
4. an independent agency of the federal government responsible for mail delivery (and sometimes telecommunications) between individuals and businesses in the United States
   同義詞：United States Post Office, US Post Office, Post Office, PO