kindergarten

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A program or class for four-year-old to six-year-old children that serves as an introduction to school.

from The Century Dictionary.

• noun A school in which instruction is imparted to very young children by the use of objects and instructive games and songs, according to the system initiated by Friedrich Froebel (1782-1852) in Germany in 1840.

from the GNU version of the Collaborative International Dictionary of English.

• noun A class within a primary school or a separate school for young children, usually between the ages of four and six years, designed to adapt children to the classroom environment before beginning academic training, on the theory that education should be begun by gratifying and cultivating the normal aptitude for exercise, play, observation, imitation, and construction; -- a name given by Friedrich Froebel, a German educator, who introduced this method of training, in rooms opening on a garden.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An educational institution for young children, usually between ages 4 and 6; nursery school.
• noun US The elementary school grade before first grade.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a preschool for children age 4 to 6 to prepare them for primary school