The quality or state of being hammy; excessive theatrical behavior or exaggeration in acting or performance.
From hammy + -ness (suffix forming abstract nouns). Emerged in 20th-century English as 'hammy' required a noun form to discuss the quality itself.
The abstractness of -ness is remarkable—we can turn almost any adjective into a concept, so 'hamminess' lets us discuss overacting as a measurable quality, which is exactly what acting coaches do when critiquing a student's performance.
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