acre

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

• noun A unit of area in the US Customary System, used in land and sea floor measurement and equal to 160 square rods, 4,840 square yards, or 43,560 square feet.
• noun Property in the form of land; estate.
• noun Archaic A field or plot of arable land.
• noun A wide expanse, as of land or other matter.

from The Century Dictionary.

• noun Originally
• noun A superficial measure of land, usually stated to be 40 poles in length by 4 in breadth; but 160 perches (= 4840 square yards, or 43,560 square feet) make an acre, however shaped.
• noun A lineal measure equal to a furrow's length, or 40 poles; more frequently, an acre's breadth, 4 poles, equal to 22 or 25 yards.

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

• noun obsolete Any field of arable or pasture land.
• noun A piece of land, containing 160 square rods, or 4,840 square yards, or 43,560 square feet. This is the English statute acre. That of the United States is the same. The Scotch acre was about 1.26 of the English, and the Irish 1.62 of the English.
• noun [Rhetorical] many acres, much landed estate.
• noun God's field; the churchyard.

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

• noun obsolete A field.
• noun A unit of surface area (symbol a. or ac.), originally as much as a yoke of oxen could plough in a day; later defined as an area 1 chain (22 yd) by 1 furlong (220 yd), or 4,840 square yards. Equivalent to about 4,046.86 square metres.
• noun in the plural, informal A large amount (of area).

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

• noun a territory of western Brazil bordering on Bolivia and Peru
• noun a town and port in northwestern Israel in the eastern Mediterranean
• noun a unit of area (4840 square yards) used in English-speaking countries