pecan

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A deciduous tree (Carya illinoinensis) of the central and southern United States, having deeply furrowed bark, pinnately compound leaves, and edible nuts.
2. n. The smooth, thin-shelled oval nut of this tree.

Century Dictionary and Cyclopedia

1. n. A North American tree, Hicoria Pecan (Carya olivæ-formis). It abounds on rich bottom-lands from Illinois southward and south westward, thriving especially in Arkansas and the Indian Territory. It is the largest tree of its genus, reaching sometimes a great height; but its wood is of little use except for fuel. Its leaves have thirteen or fifteen slender-pointed leaflets.
2. n. The nut of the pecan-tree, which is olive-shaped, an inch long or over, smooth and thin-shelled, with a very sweet and oily meat. It is gathered in large quantities for the general market.

Wiktionary

1. n. A deciduous tree Carya illinoinensis of the central and southern United States, having deeply furrowed bark, pinnately compound leaves, and edible nuts.
2. n. A smooth, thin-shelled, edible oval nut of this tree.
3. n. A half of the edible portion of the inside of this nut.

GNU Webster's 1913

1. n. (Bot.) A species of hickory (Carya olivæformis), growing in North America, chiefly in the Mississippi valley and in Texas, where it is one of the largest of forest trees; also, its fruit, a smooth, oblong nut, an inch or an inch and a half long, with a thin shell and well-flavored meat.

WordNet 3.0

1. n. wood of a pecan tree
2. n. tree of southern United States and Mexico cultivated for its nuts
3. n. smooth brown oval nut of south central United States