To dissemble is to hide under a false appearance, to deceive. "When confronted about their human rights record, the Chinese government typically dissembles."
Dissemble is a little more complicated than a straight lie or denial. When you dissemble, you disguise your true intentions or feelings behind a false appearance. To dissemble is to pretend that you don't know something, to pretend that you think one way when you act another way. "My boyfriend was dissembling the whole time. He was a married father of two."