[syn: United States Post Office, US Post Office, Post Office, PO]
The Collaborative International Dictionary of English v.0.48:
Phosphoryl \Phos"phor*yl\ (f[o^]s"f[o^]r*[i^]l), n. [Phosphorus
   + -yl.] (Chem.)
   The radical PO, regarded as the typical nucleus of certain
   compounds.
   [1913 Webster]
WordNet (r) 3.0 (2006):
Po
    n 1: 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 [syn:
         polonium, Po, atomic number 84]
    2: a noncommissioned officer in the Navy or Coast Guard with a
       rank comparable to sergeant in the Army [syn: petty
       officer, PO, P.O.]
    3: a European river; flows into the Adriatic Sea [syn: 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 [syn: United
       States Post Office, US Post Office, Post Office, PO]
V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):
PO
       Portable Object (MO)