Synonyms for Rigor (same or very similar meaning)
WordNet sense 1 (the quality of being logically valid):
cogency, validity, rigour
WordNet sense 2 (something hard to endure):
asperity, grimness, hardship, rigorousness, severeness, severity, rigourousness
WordNet sense 3 (excessive sternness):
hardness, harshness, inclemency, stiffness
From the ODE community, based on WordNet
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