The Collaborative International Dictionary of English v.0.48:

Cantor \Can"tor\, n. [L., a singer, fr. caner to sing.]
   A singer; esp. the leader of a church choir; a precentor.
   [1913 Webster]

         The cantor of the church intones the Te Deum. --Milman.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cantor
    n 1: the musical director of a choir [syn: choirmaster,
         precentor, cantor]
    2: the official of a synagogue who conducts the liturgical part
       of the service and sings or chants the prayers intended to be
       performed as solos [syn: cantor, hazan]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "cantor":
   Heldentenor, Levite, Meistersinger, alto, aria singer, baal kore,
   baritenor, baritone, bass, basso, basso buffo, basso cantante,
   basso profundo, blues singer, canary, cantatrice, caroler, chanter,
   chantress, chief rabbi, choir chaplain, choirmaster,
   choral director, chorister, coloratura soprano, comic bass,
   contralto, countertenor, crooner, deep bass, diva,
   dramatic soprano, heroic tenor, high priest, hymner, improvisator,
   kohen, lead singer, lieder singer, melodist, mezzo-soprano,
   minister of music, opera singer, precentor, priest, prima donna,
   psalm singer, rabbi, rabbin, rock-and-roll singer, scribe, singer,
   singstress, songbird, songster, songstress, soprano, tenor,
   torch singer, vocalist, vocalizer, voice, warbler, yodeler



The Free On-line Dictionary of Computing (30 December 2018):

Cantor

   1.  A mathematician.

   Cantor devised the diagonal proof of the uncountability of the
   real numbers:

   Given a function, f, from the natural numbers to the real
   numbers, consider the real number r whose binary expansion is
   given as follows: for each natural number i, r's i-th digit is
   the complement of the i-th digit of f(i).

   Thus, since r and f(i) differ in their i-th digits, r differs
   from any value taken by f.  Therefore, f is not surjective
   (there are values of its result type which it cannot return).

   Consequently, no function from the natural numbers to the
   reals is surjective.  A further theorem dependent on the
   axiom of choice turns this result into the statement that
   the reals are uncountable.

   This is just a special case of a diagonal proof that a
   function from a set to its power set cannot be surjective:

   Let f be a function from a set S to its power set, P(S) and
   let U =  x in S: x not in f(x) .  Now, observe that any x in
   U is not in f(x), so U != f(x); and any x not in U is in f(x),
   so U != f(x): whence U is not in  f(x) : x in S .  But U is
   in P(S).  Therefore, no function from a set to its power-set
   can be surjective.

   2.  An object-oriented language with fine-grained
   concurrency.

   [Athas, Caltech 1987.  "Multicomputers: Message Passing
   Concurrent Computers", W. Athas et al, Computer 21(8):9-24
   (Aug 1988)].

   (1997-03-14)