The quality or state of being congested; the condition of being overcrowded, blocked, or overfull.
From congested (past participle of congest) plus the abstract noun suffix -ness, creating a noun form that describes the state of congestion.
Adding '-ness' to adjectives is one of English's most productive word-building tricks—'congestedness' might sound awkward, but it perfectly captures that stuffy, crowded feeling!
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