Traitor, n.
Etymology: [OE. traitour, OF. traïtor, traïteur, F. treître, L. traditor, fr. tradere, traditum, to deliver, to give up or surrender treacherously, to betray; trans across, over + dare to give. See Date time, and cf. Betray,Tradition, Traditor, Treason.]
1. One who violates his allegiance and betrays his country; one guilty of treason; one who, in breach of trust, delivers his country to an enemy, or yields up any fort or place intrusted to his defense, or surrenders an army or body of troops to the enemy, unless when vanquished; also, one who takes arms and levies war against his country; or one who aids an enemy in conquering his country. See Treason. O passing traitor, perjured and unjust! Shak.
2. Hence, one who betrays any confidence or trust; a betrayer. "This false traitor death." Chaucer.
2 other Webster entries under this spelling
Traitor, a.
Traitorous. [R.] Spenser. Pope.
Traitor, v. t.
To act the traitor toward; to betray; to deceive. [Obs.] " But time, it traitors me." Lithgow.
Shades of meaning
Fernald lists traitor only as an antonym, under adherent.
He lists it without comment; the entries above explain its neighbors.