The Collaborative International Dictionary of English v.0.48:

School \School\, n. [OE. scole, AS. sc?lu, L. schola, Gr. ?
   leisure, that in which leisure is employed, disputation,
   lecture, a school, probably from the same root as ?, the
   original sense being perhaps, a stopping, a resting. See
   Scheme.]
   1. A place for learned intercourse and instruction; an
      institution for learning; an educational establishment; a
      place for acquiring knowledge and mental training; as, the
      school of the prophets.
      [1913 Webster]

            Disputing daily in the school of one Tyrannus.
                                                  --Acts xix. 9.
      [1913 Webster]

   2. A place of primary instruction; an establishment for the
      instruction of children; as, a primary school; a common
      school; a grammar school.
      [1913 Webster]

            As he sat in the school at his primer. --Chaucer.
      [1913 Webster]

   3. A session of an institution of instruction.
      [1913 Webster]

            How now, Sir Hugh! No school to-day?  --Shak.
      [1913 Webster]

   4. One of the seminaries for teaching logic, metaphysics, and
      theology, which were formed in the Middle Ages, and which
      were characterized by academical disputations and
      subtilties of reasoning.
      [1913 Webster]

            At Cambridge the philosophy of Descartes was still
            dominant in the schools.              --Macaulay.
      [1913 Webster]

   5. The room or hall in English universities where the
      examinations for degrees and honors are held.
      [1913 Webster]

   6. An assemblage of scholars; those who attend upon
      instruction in a school of any kind; a body of pupils.
      [1913 Webster]

            What is the great community of Christians, but one
            of the innumerable schools in the vast plan which
            God has instituted for the education of various
            intelligences?                        --Buckminster.
      [1913 Webster]

   7. The disciples or followers of a teacher; those who hold a
      common doctrine, or accept the same teachings; a sect or
      denomination in philosophy, theology, science, medicine,
      politics, etc.
      [1913 Webster]

            Let no man be less confident in his faith . . . by
            reason of any difference in the several schools of
            Christians.                           --Jer. Taylor.
      [1913 Webster]

   8. The canons, precepts, or body of opinion or practice,
      sanctioned by the authority of a particular class or age;
      as, he was a gentleman of the old school.
      [1913 Webster]

            His face pale but striking, though not handsome
            after the schools.                    --A. S. Hardy.
      [1913 Webster]

   9. Figuratively, any means of knowledge or discipline; as,
      the school of experience.
      [1913 Webster]

   Boarding school, Common school, District school,
   Normal school, etc. See under Boarding, Common,
      District, etc.

   High school, a free public school nearest the rank of a
      college. [U. S.]

   School board, a corporation established by law in every
      borough or parish in England, and elected by the burgesses
      or ratepayers, with the duty of providing public school
      accommodation for all children in their district.

   School committee, School board, an elected committee of
      citizens having charge and care of the public schools in
      any district, town, or city, and responsible for control
      of the money appropriated for school purposes. [U. S.]

   School days, the period in which youth are sent to school.


   School district, a division of a town or city for
      establishing and conducting schools. [U.S.]

   Sunday school, or Sabbath school, a school held on Sunday
      for study of the Bible and for religious instruction; the
      pupils, or the teachers and pupils, of such a school,
      collectively.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sunday \Sun"day\, a.
   Belonging to the Christian Sabbath.
   [1913 Webster]

   Sunday letter. See Dominical letter, under Dominical.


   Sunday school. See under School.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Sunday school
    n 1: school meeting on Sundays for religious instruction [syn:
         Sunday school, Sabbath school]