2. (noun)dad, dada, daddy, pa, papa, pappa, pop an informal term for a father; probably derived from babytalk
3. (noun)protactinium, protoactinium, Pa, atomic number 91 a short-lived radioactive metallicelement formed from uranium and disintegrating into actinium and then into lead
5. (noun)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"