The Collaborative International Dictionary of English v.0.48:

Pa \Pa\ (p[aum]), n.
   A shortened form of Papa.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

The Free On-line Dictionary of Computing (19 January 2023):

pa

    The country code for Panama.

   (1999-01-27)