Disloyalty

Noun

 * 1)  An act of being disloyal; a betrayal.
 * 2)  The opposite of loyalty.

Thesaurus
Punic faith, apostasy, backsliding, bad faith, barratry, betrayal, bolt, breach of faith, breach of promise, breach of trust, breakaway, defection, dereliction, desertion, disaffection, faithlessness, falseness, falsity, fickleness, going over, inconstancy, infidelity, mala fides, perfidiousness, perfidy, ratting, recidivation, recidivism, recreancy, secession, treacherousness, treason, trothlessness, turning traitor, unfaith, unfaithfulness, unloyalty, unsteadfastness, untrueness

Etymology
desloiauté: (Modern déloyauté:) from des-: + loiauté: