Knight service : A tenure of lands held by knights on condition of performing military service. See Chivalry, n., 4.

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Taxonomy
knight-service, knights, tenure, military service, lands, scutage, fief, barons, England, lords, free encyclopedia, English, liability, fees, obligation, king, marriage, Exchequer.

Defination from the web:
knight-service was developed out of the liability, under the English system, of every five hides to provide one soldier ... charter of Henry I (1100), which speaks of those holding by knight-service as "milites qui per loricam terras sues deserviunt. ...