Unsteadfastly is an adverb that describes someone or something that lacks stability or consistency. Some synonyms for this word include unfaithfully, fleetingly, inconsistently, erratically, impulsively, capriciously, mercurially, or volatilely. All of these words imply a lack of steadfastness or reliability, which can be problematic in many situations, particularly in relationships or in business dealings. By using synonyms for the word unsteadfastly, you can add variety and complexity to your writing while also conveying the same idea that the person or thing is not trustworthy or reliable.