E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
¶ Sword (phrases and proverbs).
At swords point. In deadly hostility, ready to fight each other with swords.
Poke not fire with a sword. This was a precept of Pythagoras, meaning add not fuel to fire, or do not irritate an angry man by sharp words which will only increase his rage. (See Iamblichus Protreptics, symbol ix.)
To put to the sword. To slay.
Your tongue is a double-edged sword.
You first say one thing and then the contrary; your argument cuts both ways. The allusion is to the double-edged sword out of the mouth of the Son of Manone edge to condemn, and the other to save. (Rev. i. 16.)
Yours is a Delphic swordit cuts both ways. Erasmus says a Delphic sword is that which accommodates itself to the pro or con. of a subject. The reference is to the double meanings of the Delphic oracles, called in Greek Delphik muchaira.