a treacherous breach of faith: a betrayal of a bond one was trusted to keep, toward God or toward another person
This word names an act of treachery. Not just any wrong, but the specific wrong of betraying a trust that someone was counted on to keep. A person commits it by breaking faith with God, by laying hands on what is holy, or by deceiving a neighbor who trusted them. The common thread is the broken bond, which is why English Bibles reach for words like trespass, unfaithfulness, treachery, and transgression to translate it.
Most often the betrayed party is God. Israel's covenant is treated as a bond of loyalty, so idolatry, rebellion, and abandoning the LORD are all called this kind of treachery. A striking sub-use is sacrilege: taking or misusing something set apart for God, whether the devoted spoils of a captured city or the vessels of the temple, counts as a breach of faith because those things belonged to him.
The same word also covers betrayal between people. Cheating a neighbor by swearing a false oath over a deposit, or a wife being unfaithful to her husband, are each this treachery on a human scale. In one poetic case the word describes faithless, unreliable speech. Across all of these the core holds steady: a trust was given, and it was broken.