Petard

Petard is almost always used in only one context – to be hoist by one’s own petard. The line comes from a little-known Elizabethan playwright called William Shakespeare, whom a few of you may have heard of. The line is from Hamlet, Act 3, Scene 4 and is spoken by the eponymous hero in a passage relating to the plot by Rosencrantz and Guildenstern (his erstwhile friends) to have him killed:

There’s letters seal’d; and my two schoolfellows,
Whom I will trust as I will adders fang’d,
They bear the mandate; they must sweep my way
And marshal me to knavery. Let it work;
For ’tis the sport to have the enginer
Hoist with his own petar; and ‘t shall go hard
But I will delve one yard below their mines
And blow them at the moon. O, ’tis most sweet
When in one line two crafts directly meet.

Before the description of the phrase, let’s delve a little into the etymology, which in itself is amusing in a schoolboy-ish fashion. The word in modern form derives from the Latin peditum, which in turn became péter in Old and Middle French. The meaning of these is “a loud expulsion of intestinal gases” – simply put, a fart. The French version was put to use to form pétard – a small conical mortar bomb device used by weapons engineers from Mediaeval times onwards to blow holes in walls and gates when attempting to penetrate a castle’s defences. A small trench or pit would be dug and the pétard placed on a supporting beam inside it. A crude throwing device would be used to hurl it up at the wall or gate in the hope of causing enough damage to break through

Now the tricky bit. I will attempt – without the aid of a safety net – to interpret just what old Will was on about. The gist of the passage is that the letters referred to by Hamlet contain a warrant for his own death, owing to a little chicanery by Rosencrantz and Guildenstern. He later opens the letters and amends them so it looks as thought the warrant is for the deaths of his old school chums. He talks of “delving below their mines” – which suggests he will change the letters and beat them at their own game. So the engineers of the subterfuge would be hoist (or blown into the air) by their own petar, as he spells it. The phrase is a metaphor for anyone caught out by their own trick or trap. I still think it would have been easier if he’d just said that in the first place.