say it: SIR-ee-uh-snuhs
seriousness is a noun meaning "an earnest and sincere feeling". It carries 3 recorded senses.
an earnest and sincere feeling
the quality of arousing fear or distress
“he learned the seriousness of his illness”
the trait of being serious
“a lack of solemnity is not necessarily a lack of seriousness”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for seriousness come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.