The amount that a gourd can hold; a gourd used as a measure or container filled to capacity.
From gourd + -ful (suffix meaning 'the amount that can be held'), following the pattern of cupful, handful, spoonful, etc.
Before standardized measurements, 'a gourdful' or 'a handful' or 'a basketful' were actual legitimate units of measure—different gourds held different amounts, which is why merchants eventually demanded standardized weights and measures.
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