double-edged sword

Meaning

Noun

• A benefit that is also a liability, or (a benefit) that carries some significant but not-so-obvious cost or risk.

Origin

• From the notion that if two sides of the same blade are sharp, it cuts both ways. The metaphor may have originated from the expression سَيْفٌ ذُو حَدَّيْنِ.
• The metaphor is first attested to in English in the 15th century. It is not to be confused with a double-ended sword.