Answer: rigorous

AnswerCrossword Clue
RIGOROUSDemanding
RIGOROUSHarsh.
RIGOROUSInexorable
RIGOROUSHarsh or severe
RIGOROUSDisciplined
rigorousrigidly severe or harsh, as people, rules, or discipline
rigorouscharacterized by rigor
rigorous(of weather or climate) uncomfortably severe or harsh; extremely inclement
rigorousseverely exact or accurate; precise
rigorouslogically valid