fealty derives from the French word foi meaning faith or trust. In the Middle Ages those in power demanded oaths of fealty from those subject to them—kings from their officials and their nobility (as William the Conqueror seems to have demanded at Salisbury in 1086), prelates from their clergy, manorial lords from their peasants—in order to confirm and strengthen their authority, perhaps at moments of crisis or challenge. Unlike homage, fealty was a unilateral process: those to whom oaths were given were not obliged to promise anything in return.

Anne Curry

fe·al·ty / ˈfēltē/ • n. hist. a feudal tenant's or vassal's sworn loyalty to a lord: they owed fealty to the Earl rather than the King. ∎  formal acknowledgment of this: a property for which she did fealty.

fealty obligation of fidelity. XIV. ME. fe(a)ute, fealtie — OF. feau(l)te, fealte (mod. féauté) :- L. fidēlitās, -āt-, f. fidēlis faithful, f. fidēs FAITH; see -TY2.