The Collaborative International Dictionary of English v.0.48:

Acre \A"cre\, n. [OE. aker, AS. [ae]cer; akin to OS. accar, OHG.
   achar, Ger. acker, Icel. akr, Sw. [*a]ker, Dan. ager, Goth.
   akrs, L. ager, Gr. ?, Skr. ajra. [root]2, 206.]
   1. Any field of arable or pasture land. [Obs.]
      [1913 Webster]

   2. 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.
      [1913 Webster]

   Note: The acre was limited to its present definite quantity
         by statutes of Edward I., Edward III., and Henry VIII.
         [1913 Webster]

   Broad acres, many acres, much landed estate. [Rhetorical]


   God's acre, God's field; the churchyard.
      [1913 Webster]

            I like that ancient Saxon phrase, which calls
            The burial ground, God's acre.        --Longfellow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

acre
    n 1: a unit of area (4840 square yards) used in English-speaking
         countries
    2: a territory of western Brazil bordering on Bolivia and Peru
    3: a town and port in northwestern Israel in the eastern
       Mediterranean [syn: Acre, Akko, Akka, Accho]

Easton's 1897 Bible Dictionary:

Acre
   is the translation of a word (tse'med), which properly means a
   yoke, and denotes a space of ground that may be ploughed by a
   yoke of oxen in a day. It is about an acre of our measure (Isa.
   5:10; 1 Sam. 14:14).


Bouvier's Law Dictionary, Revised 6th Ed (1856):

ACRE, measures. A quantity of land containing in length forty perches, and
four in breadth, or one hundred and sixty square perches, of whatever shape
may be the land. Serg. Land Laws of Penn., 185. See Cro. Eliz. 476, 665; 6
Co. 67; Poph. 55; Co. Litt. 5, b, and note 22.