prairie

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An extensive area of flat or rolling, predominantly treeless grassland, especially the large tract or plain of central North America.

Century Dictionary and Cyclopedia

1. n. A meadow; level grassy land: a word frequently used by Hennepin and other French writers in describing the country adjacent to the Mississippi river, and now in common use, designating the level or slightly undulating treeless areas which cover a large part of Illinois, Wisconsin, Iowa, Minnesota, and other States further south. The prairies are never by the inhabitants of the prairie regions called plains, as are the treeless regions further west. They are characterized by a highly fertile soil, often of great thickness, and they often occur where the rainfall is even considerably larger than on parts of the adjacent forest-covered regions. The cause of the absence of trees upon them cannot, therefore, be deficiency of moisture; in all probability it is the physical character of the soil, and especially its extreme flneness, which renders it more suitable for the growth of the grasses than for that of arboreal vegetation. In the extreme northwestern region of the United States, especially in Montana, certain level treeless areas surrounded by the mountains are now by some called prairies: some of these had been previously denominated holes. Further south in the Rocky Mountains they are known as parks, or sometimes as basins. See hole, 6, and plain.
2. n. Any small open space in a forest. See the extract.

Wiktionary

1. n. An extensive area of relatively flat grassland with few, if any, trees, especially in North America.

GNU Webster's 1913

1. n. An extensive tract of level or rolling land, destitute of trees, covered with coarse grass, and usually characterized by a deep, fertile soil. They abound throughout the Mississippi valley, between the Alleghanies and the Rocky mountains.
2. n. A meadow or tract of grass; especially, a so called natural meadow.

WordNet 3.0

1. n. a treeless grassy plain