An idle threat is a statement or promise made without any intention of following through. There are a number of synonyms for this phrase including empty threat, hollow promise, vain declaration, and meaningless statement. These synonyms all share the common feature of referring to the use of words without any real intent to act upon them. Other synonyms for idle threat might include insincere commitment, false assertion, or empty words. Regardless of the specific phrasing, an idle threat is something that should be taken seriously, as it can often serve as a warning sign of immature or irresponsible behavior.