Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
rustiness is a noun meaning "the condition of being coated or clogged with rust". It carries 2 recorded senses.
the condition of being coated or clogged with rust
ineptitude or awkwardness as a consequence of age or lack of practice
“his rustiness showed when he was asked to speed up”
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 rustiness come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.