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.
To betray or go back on.
faithfulness
noun
The state of being faithful
How often have the words double-cross and faithfulness occurred in a corpus of books? (source: Google Ngram Viewer )