Treachery, n.
Etymology: [OE. trecherïe, trichere, OF. trecherie, tricherie, F. tricherie trickery, from tricher to cheat, to trick, OF. trichier, trechier; probably of Teutonic origin. See Trickery, Trick.]
Violation of allegiance or of faith and confidence; treasonable or perfidious conduct; perfidy; treason.
Be ware, ye lords, of their treachery. Chaucer. In the council chamber at Edinburgh, he had contracted a deep taint of treachery and corruption. Macaulay.
Shades of meaning
Fernald has no entry of its own for treachery; he lists it under fraud.
Where he writes about it:
Treachery is chiefly used of dishonesty in matters of friendship, social relations, government, or war; treachery may be more harmful than fraud, but is not so gross, and is not ordinarily open to legal redress. — from fraud
Treason is a specific form of treachery of a subject to the government to which he owes allegiance, and is definable and punishable at law. — from fraud