falsehood: that which has no truth or reality behind it, whether a spoken lie, a betrayal in action, or a hope that comes to nothing
At its core this word names the gap between what something claims and what is real. Most often that gap is a lie: words said to deceive, a witness who testifies to what did not happen, an oath sworn with no intention of keeping it. It is the standard biblical word for the false prophet, who speaks his own message and stamps God's name on it.
But the same word reaches past speech to action and even to outcomes. A person can deal in falsehood, repaying good with betrayal, behaving as someone they are not. And a thing can be falsehood when it simply fails: a horse trusted for rescue, an idol that promises and delivers nothing. In every case the word marks a claim that collapses under reality.
Hebrew frequently uses it adverbially, as a charge against how something is done: to swear falsely, to deal falsely, to prophesy falsely. The senses below sort this range, but they all share one center, the absence of truth where truth was claimed.