Such a large number, as in There were so many guests that we didn't have enough chairs. [ First half of 1200s ]
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An unspecified number, as in There allegedly are so many shrimp per pound, but of course the exact number depends on their size and weight. [ First half of 1500s ]
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Forming a group, as in The reporters turned on the speaker like so many tigers let loose. [ c. 1600 ]