E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Swear
now means to take an oath, but the primitive sense is merely to aver or affirm; when to affirm on oath was meant, the word oath was appended, as “I swear by oath.” Shakespeare uses the word frequently in its primitive sense; thus Othello says of Desdemona—
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“She swore, in faith, ’twas strange, ’twas passing strange.”
