WordNet sense 1 (a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead):

protactinium, protoactinium

WordNet sense 2 (a unit of pressure equal to one newton per square meter):

pascal

WordNet sense 3 (an informal term for a father; probably derived from baby talk):

dad, daddy, papa, pop, dada, pappa

WordNet sense 4 (a Mid-Atlantic state; one of the original 13 colonies):

Pennsylvania, Keystone State

WordNet sense 5 (an electronic amplification system used as a communication system in public areas):

P.A., public address system, P.A. system, PA system