s. Severidad, calidad de severo (riguroso, sin indulgencia; que muestra gran rigor; que muestra gran regularidad pero pocos adornos)

extreme plainness: austereness, plainness, severity
excessive sternness: harshness, stiffness, strictness, severity, sternness, inclemency, rigor, rigorousness, rigour, hardness, rigourousness
something hard to endure: hardship, rigourousness, difficultness, difficulty, sternness, rigor, rigorousness, rigour, asperity, grimness, severity
used of the degree of something undesirable e.g. pain or weather: distressfulness, severity, raininess, seriousness, intensity, intensiveness, badness, foulness