adj.

steadfast; uncompromising; inexorable; inflexible ((of a person) never yielding or giving way); unbending; rigid; intransigent; determined (stubborn • He's very determined); dour; grim (stubborn, unyielding • grim determination); relentless; steely; stiff; lockstep; never-say-die; rock-ribbed; unbendable; unpersuadable; unstoppable (о стремлении); unyielding; cast iron; strong-minded; intransigeant; stern; unmoved; stubborn (Aly19); staunch (Aly19); diehard (grafleonov); die-hard (grafleonov); never say die; rock ribbed; hardshell; sticky; unrelenting; quite firm (linton); cast-iron; defiant (He's taken a defiant stand/stance on the issue. VLZ_58); final (о тоне alikssepia); adamant (determined or insistent • adamant to entreaties – непреклонный к мольбам; an adamant refusal); Catonian; deadly (ssn); doctrinaire (Екатерина Лебедева); unshakable (Abysslooker); deaf; headstrong; rude; stiff necked; unbowed; unlimber; unpliable; unbend; opinionated (Ivan Pisarev); dogmatic (Ivan Pisarev); biased (Ivan Pisarev); bigoted (Ivan Pisarev); bossy (Ivan Pisarev); bullheaded (Ivan Pisarev); cocksure (Ivan Pisarev); conceited (Ivan Pisarev); dictatorial (Ivan Pisarev); dogmatical (Ivan Pisarev); hardline (Ivan Pisarev); obstinate (Ivan Pisarev); pigheaded (Ivan Pisarev); self-assertive (Ivan Pisarev)

adamantine (unyielding; inflexible; "If there is one dominant trait that emerges from this account, it is adamantine willpower" [Eugene Linden])