* επίμονος (epímonos): This translates to "persistent" or "insistent," and often implies a positive connotation of determination. It's a good choice if the stubbornness is directed towards a worthy goal.
* πεισματάρης (peismatáris): This is a more common and generally accepted word for "stubborn," often implying a negative connotation of being headstrong and unwilling to compromise. It's probably the closest single-word equivalent.
* αμετανόητος (ametanóitos): This means "unrepentant" or "unyielding," suggesting stubbornness in the face of criticism or evidence to the contrary.
* δύσκαμπτος (dýskamptos): This translates to "inflexible" or "rigid," highlighting the unwillingness to change one's mind or adapt.
The best word to use will depend on the context. For most situations, πεισματάρης (peismatáris) is a safe and accurate choice.