Learn how to say Rigorousness correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word rigorous:
extremely thorough and careful:
the rigorous testing of consumer products
(of a rule, system, etc.) strictly applied or adhered to:
rigorous controls on mergers
(of a person) adhering strictly to a belief or system:
a rigorous teetotaller
harsh and demanding:
many of the expedition had passed rigorous SAS courses
late Middle English: from Old French rigorous or late Latin rigorosus, from rigor ‘stiffness’ (see rigor1)
If a word ends in -our (in this case rigour), change -our to -or before adding -ous and some other endings: rigorous.