Wiktionary
n. (context idiomatic English) A benefit that is also a liability, or that carries some significant but non-obvious cost or risk.
Wikipedia
"Double-Edged Sword" is the fourteenth episode of the fifth season of the American television comedy series 30 Rock, and the 94th overall episode of the series. It was directed by Don Scardino, and written by Kay Cannon & Tom Ceraulo. The episode originally aired on the National Broadcasting Company (NBC) network in the United States on February 10, 2011. Guest stars in this episode include Elizabeth Banks, John Cho, and Matt Damon.
In this episode, Jack Donaghy ( Alec Baldwin) heads to Toronto with his wife, Avery ( Elizabeth Banks). When she goes into labor, they try their best to get back to the United States with the help of a meth smuggler, Lorne ( John Cho). Meanwhile, Liz Lemon ( Tina Fey) boards a plane with her boyfriend, Carol ( Matt Damon), as the pilot. Things do not go well when the plane has not flown yet and Carol keeps telling them that they will leave "in about half an hour" several times. Elsewhere, Tracy Jordan ( Tracy Morgan) deals with the pressure of having won an EGOT and the formal expectations that he has to meet.
Usage examples of "double-edged sword".
He wore a knee-length chainmail hauberk and steel strips on leather armguards, a plain double-edged sword at his waist.
He had stowed his bow and now had a short double-edged sword in his hand.
He'd always understood that he held a dangerous double-edged sword in his hand.
There was the leaping flame standard of Brandan and the stooping hawk of Edirr, Jaran's stricken tree, and the Coman's double-edged sword flying over a token force: the rest would be waiting down river at Kraggen Keep, as would be Ardeth's at Omiroth and the Edirr twins' at Kestrie.
He drew the long double-edged sword at his waist and led the way at a run, moving with practiced agility despite the sixty pounds of alloy-steel protection, an extra sword and a heater-type shield slung over his back.
Love spells, sleep spells, invisibility spells: these she had no fear of, and the scent of almond seemed to her like a veil, one that worked as a double-edged sword in her favor.
On one shapely hip she wore a straight double-edged sword, and on the other a long dirk.
Now we see that power ultimately proved a double-edged sword, as its loss brought disaster to Toremal's Emperors at the height of their powers.
I wanted them to see the statue rolling around on the floor of the front seat, but having them this close was a double-edged sword.
Smiling, he drew his long, double-edged sword from his scabbard, held it like a merchant's balance.
The bloodred seal was Maybor's: the swan and the double-edged sword.
It drew a huge, double-edged sword and continued its flight up the trail, dragging Mali with it.
He took my straight, double-edged sword from one of his human slaves and bared it.