Flintiness refers to a quality of being tough, unyielding, and resolute, like the mineral flint. Synonyms for flintiness include hardness, rigidity, firmness, steadfastness, and determination. It's a personality trait that denotes a strong, unbreakable character that is not easily swayed or influenced by others. The word flintiness can also imply a level of harshness or severity, which can be used in a positive sense to describe someone who is clear and direct in their actions or in a negative sense to describe someone who is cold, unfeeling, and unapproachable. In any case, the synonyms for flintiness capture a sense of unwavering strength and resolve that is admired by many.