noun
An English unit of land area (symbol: a. or ac.) originally denoting a day's ploughing for a yoke of oxen, now standardized as 4,840 square yards or 4,046.86 square metres.
Any of various similar units of area in other systems.
(informal, usually in the plural) A wide expanse.
(informal, usually in the plural) A large quantity.
(obsolete) A field.
(obsolete) The acre's breadth by the length, English units of length equal to the statute dimensions of the acre: 22 yd (≈20 m) by 220 yd (≈200 m).
(obsolete) A duel fought between individual Scots and Englishmen in the borderlands.