Answer: severest

AnswerCrossword Clue
SEVERESTMost austere
SEVERESTExtreme to the extreme
SEVERESTStrict to the extreme
SEVERESTMost rigid
SEVERESTMost rigorous.
SEVERESTA kind of critic.
SEVEREST"Dearest friend, ... critic."
SEVERESTMost keen.
SEVERESTHarshest.
SEVERESTGravest
SEVERESTMost harsh
severest(of something bad or undesirable) Very great; intense
severestVery plain in style or appearance
severestStrict or harsh
severestSEVERE, harsh (severe)
severestDemanding great ability, skill, or resilience