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 -
“She swore, in faith, `twas strange, `twas passing strange.”
Othello, i. 3.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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