say it: FIT-nuhs
fitness is a noun meaning "the quality of being suitable". It carries 3 recorded senses.
the quality of being suitable
“they had to prove their fitness for the position”
good physical condition; being in shape or in condition
the quality of being qualified
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 fitness 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.