1. (noun) public address system, P.A. system, PA system, P.A., PA
an electronic amplification system used as a communication system in public areas
2. (noun) dad, dada, daddy, pa, papa, pappa, pop
an informal term for a father; probably derived from baby talk
3. (noun) protactinium, protoactinium, Pa, atomic number 91
a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead
4. (noun) pascal, Pa
a unit of pressure equal to one newton per square meter
5. (adverb) Pennsylvania, Keystone State, PA
a Mid-Atlantic state; one of the original 13 colonies
6. (adverb) per annum, p.a., per year, each year, annually
by the year; every year (usually with reference to a sum of money paid or received)
"he earned $100,000 per annum"; "we issue six volumes per annum"
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Definitions of P.A. 
