from The American Heritage® Dictionary of the English Language, 4th Edition
- transitive v. To betray by acting in contradiction to a prior agreement. See Synonyms at deceive.
- n. An act of betraying an ally, a friend, or an associate.
- n. Genetics A cross in which each parent is the product of a single cross. It can be represented as AB × CD, where A, B, C, and D are inbred lines.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To betray or go back on
First recorded in 1834 from thieves' slang cross (or on the cross) to refer to something dishonest, a play on straight/square, and therefore a crook going back on his partners would be crossing the crossers, or double-crossing. (Wiktionary)