noun

an uncompromising adherence to a firm policy.

he is known to take a hard line on sentencing policy for murder

adjective

uncompromising; strict.

a hard-line party activist

uncompromising,strict,diehard,extreme,tough,inflexible,immoderate,intransigent,intractable,unyielding,undeviating,unwavering,single-minded,not giving an inch,indurate