The quality or state of being unwilling to give, grant, or do something; the character of holding or expressing resentment.
From the adjective 'grudging' plus the noun-forming suffix '-ness', which transforms qualities or states of being into countable nouns. Common pattern in English for creating abstract nouns.
The '-ness' suffix is one of English's most productive ways to turn feelings into things we can discuss—turning an emotion into an abstract noun lets us debate whether grudgingness is justified or destructive!
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