The standard modern plural of cupful, meaning multiple cups worth of something.
From cupful + -s plural. Modern English prefers pluralizing the measure word (cupfuls) over the measured item, becoming the accepted standard by the 20th century.
Language evolution in action: 'cupfuls' won the plural battle because it sounds less ridiculous than 'cupfulfuls'—modern English just picks the option that doesn't make people giggle!
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