1. conceal something, hide one's true feelings, appearance or beliefs
If you 'dissemble' something it means to take on the guise or pretence of something else. To dissemble implies an element of deceit, the phrase, therefore, has a negative connotation. "She dissembled sympathy for her client then rushed out to profit from her findings." "Do not dissemble the facts with us. We are aware of the reality all too well." This is a formal expression usually used in professional contexts.