1
general::
Phrase(s): double-cross someone
to betray someone. (Originally a more complicated switching of sides in a conspiracy wherein the double-crosser sides with the victim of the conspiracy—against the original conspirator.) • Don’t even think about double-crossing me! • Richard doublecrossed Mr. Big a few years back.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
A deliberate betrayal; violation of a promise or obligation, as in They had planned a double cross, intending to keep all of the money for themselves. This usage broadens the term's earlier sense in sports gambling, where it alluded to the duplicity of a contestant who breaks his word after illicitly promising to lose. Both usages gave rise to the verb double-cross. [Late 1800s]
American Heritage Idioms