n. (context cryptography dated English) Any predictable facet of the http://en.wikipedia.org/wiki/Enigma%20Machine cipher due to operator error or laziness, whose existence helped the Allies to break the code.
Cilly can refer to:
- an alternative spelling of Celje, the third largest city in Slovenia
- Cilly, Aisne, a commune of the Aisne département in northern France
- Cilly Aussem (1909–1963), German female tennis player