double-cross

To betray or go back on; to deceive someone after having gained their trust and led them to believe that they were being aided.

If you double-cross us, we'll track you down and kill you.

To cross twice in hybridization, as (A × B) × (C × D); for example, in commercial hybrid seed corn, A through D are classically inbreds, and their grandoffspring is the seed for sale.

An instance of betrayal of one who had been led to believe that the betrayer was assisting them.

The hybrid product of double-crossing.