From The Collaborative International Dictionary of English v.0.48:

Abbey Ab"bey ([a^]b"b[y^]), n.; pl. Abbeys (-b[i^]z). [OF. aba["i]e, abba["i]e, F. abbaye, L. abbatia, fr. abbas abbot. See Abbot.] 1. A monastery or society of persons of either sex, secluded from the world and devoted to religion and celibacy; also, the monastic building or buildings. [1913 Webster] Note: The men are called monks, and governed by an abbot; the women are called nuns, and governed by an abbess. [1913 Webster] 2. The church of a monastery. [1913 Webster] Note: In London, the Abbey means Westminster Abbey, and in Scotland, the precincts of the Abbey of Holyrood. The name is also retained for a private residence on the site of an abbey; as, Newstead Abbey, the residence of Lord Byron. [1913 Webster] Syn: Monastery; convent; nunnery; priory; cloister. See Cloister. [1913 Webster]

From WordNet (r) 2.0:

abbey n 1: a church associated with a monastery or convent 2: a convent ruled by an abbess 3: a monastery ruled by an abbot

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

ABBEY, abbatia, is a society of religious persons, having an abbot or abbess to preside over them. Formerly some of the most considerable abbots and priors in England had seats and votes in the house of lords. The prior of St. John's of Jerusalem, was styled the first baron of England, in respect to the lay barons, but he was the last of the spiritual barons.