feud

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

• noun A bitter, often prolonged quarrel or state of enmity, especially such a state of hostilities between two families or clans.
• intransitive verb To carry on or perpetuate a bitter quarrel or state of enmity.

from The Century Dictionary.

• noun In feudal law, an estate in land granted on condition of services to be rendered to the grantor, in default of which the land was to revert to the grantor; a fief; a tenure of land under and by dependence on a superior.
• noun Land held in feudal tenure by a vassal.
• noun Enmity; animosity; active hostility; a vengeful quarrel between individuals or parties; especially, hostility between families or parties in a state; a state of civic contention.
• noun More specifically, an aggravated state of hostility, marked by frequent or occasional sanguinary conflicts, between one family or clan and another, to avenge insults, injuries, or murders inflicted by one party, or by any member of it, upon those of the other side; a vendetta.

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

• noun A combination of kindred to avenge injuries or affronts, done or offered to any of their blood, on the offender and all his race.
• noun A contention or quarrel; especially, an inveterate strife between families, clans, or parties; deadly hatred; contention satisfied only by bloodshed.
• noun (Law) A stipendiary estate in land, held of a superior, by service; the right which a vassal or tenant had to the lands or other immovable thing of his lord, to use the same and take the profits thereof hereditarily, rendering to his superior such duties and services as belong to military tenure, etc., the property of the soil always remaining in the lord or superior; a fief; a fee.

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

• noun An estate granted to a vassal by a feudal lord in exchange for service
• noun A state of long-standing mutual hostility.
• noun professional wrestling slang In professional wrestling, when two rival wrestlers engage in a series of matches; often has an angle tied to it.
• verb intransitive To carry on a feud.

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

• verb carry out a feud
• noun a bitter quarrel between two parties