The Collaborative International Dictionary of English v.0.48:

Es \Es\ n.
   the chemical symbol for einsteinium, a transuranic element
   with atomic number 99. The atomic weight of the longest-lived
   isotope, with a half-life of 276 days, is 254. The first
   isotope discovered, having atomic weight 253 and a half-life
   of 20 days, was recognized in 1952 in the debris from a
   hydrogen bomb test. As much as 3 micrograms of einsteinium
   were produced by a complex process involving long irradiation
   of plutonium isotopes in nuclear reactors. Its chemical
   properties are those of a trivalent actinide element. --HCP61

   Syn: einsteinium, atomic number 99.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

Es
    n 1: a radioactive transuranic element produced by bombarding
         plutonium with neutrons [syn: einsteinium, Es, E,
         atomic number 99]

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

es

   1.  The country code for Spain.

   2.  Extensible Shell.

   3. (Expert System) An expert system for the IBM PC
   featuring forward chaining, backward chaining and fuzzy
   set relations.

   (ftp://ftp.uu.net/pub/ai/expert-sys/summers.tar.Z).

   [BYTE Oct 1990].

   (1999-02-01)