double-edged sword

Meanings

1. A benefit that is also a liability, or (a benefit) that carries some significant but not-so-obvious cost or risk.
2. A neutral principle that has applications that may be either positive (beneficial) or negative (adverse) to one's own interests.
3. Used other than figuratively or idiomatically: see double-edged, sword.

Etymology

From the notion that if two sides of the same blade are sharp, it cuts both ways. The metaphor may have originated from the Arabic expression سَيْفٌ ذُو حَدَّيْنِ (sayfun ḏū ḥaddayni, “double-edged sword”) or from the Hebrew expression חֶרֶב פִּיפִיּוֹת (ẖérev pifiyót, “double-mouthed sword”). The metaphor is first attested in English in the 15th century.