The quality or state of being croupy; the condition of being affected by or resembling croup or croupy symptoms.
From croupy (adjective) + -ness (abstract noun suffix). This creates an abstract noun describing the characteristic state or quality of having croup-like symptoms.
English -ness suffix is magical—it can turn any adjective into an abstract concept, so 'croupiness' is literally 'the quality of sounding like a sick seal,' parents everywhere understand!
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