To reveal one’s true motives or intentions. This term, like laying one’s cards on the table, comes from card-playing. Edmund Campion used a version of it in 1581: “I would I might be suffered to shewe my cardes” (Conferences Held in the Tower of London with Ed. Campion, Jesuit, cited by OED). A variant is to tip one’s hand, of the same provenance. The Economist used it on November 17, 1979: “Mr Hunt will not tip his hand on the price at which he will buy more bullion.”