The Collaborative International Dictionary of English v.0.48:

Ca \Ca\ n.
   the chemical symbol for calcium, the fifth most abundant
   element in the earth's crust, having an atomic number of 20.

   Syn: calcium.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

circa \cir"ca\ (s[~e]r"k[.a]), adv., prep. [L.]
   Approximately; about; commonly abbreviated ca.; -- used
   especially before dates and numerical measures; as, he was
   born circa 1650; ca. 50 feet high.

   Syn: ca.
        [PJC]

WordNet (r) 3.0 (2006):

Ca
    n 1: a white metallic element that burns with a brilliant light;
         the fifth most abundant element in the earth's crust; an
         important component of most plants and animals [syn:
         calcium, Ca, atomic number 20]
    2: a state in the western United States on the Pacific; the 3rd
       largest state; known for earthquakes [syn: California,
       Golden State, CA, Calif.]

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

CA

   1.  cellular automaton.

   2.  Computer Associates.

   3.  Certificate Authority.


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

ca

    The country code for Canada.

   (1995-04-19)