grand piano

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

• noun A piano having the strings strung in a horizontal harp-shaped frame supported usually on three legs.

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

• noun music A large piano in which the strings are strung horizontally in a heavy frame shaped like a harp

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

• noun a piano with the strings on a horizontal harp-shaped frame; usually supported by three legs