from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A benefit that is also a liability, or that carries some significant but non-obvious cost or risk.
From the notion that two sides of the same blade are sharp — it cuts both ways. Its origin is from the same Arabic expression سيف ذو حدين (sayf zou hadayn, "double-edged sword"). The term is first attested in the 15th century. It is not to be confused with a double-ended sword. (Wiktionary)