名詞 p.a.:

1. an electronic amplification system used as a communication system in public areas
   同義詞：public address system, P.A. system, PA system, PA
2. an informal term for a father; probably derived from baby talk
   同義詞：dad, dada, daddy, pa, papa, pappa, pop
3. a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead
   同義詞：protactinium, protoactinium, Pa, atomic number 91
4. a unit of pressure equal to one newton per square meter
   同義詞：pascal, Pa
5. a Mid-Atlantic state; one of the original 13 colonies
   同義詞：Pennsylvania, Keystone State, PA

副詞 p.a.:

1. by the year; every year (usually with reference to a sum of money paid or received)
   同義詞：per annum, per year, each year, annually