The adverb: doing something — usually looking, staring, listening, or nodding — while not understanding. It fixes itself to verbs of seeing and hearing almost exclusively: he stared uncomprehendingly, she blinked uncomprehendingly at the screen. That narrow habit is worth knowing, because it means the word paints a scene rather than states a fact. There is often something touching in it — the person is trying, but the meaning will not come. It is a long word for written English; in speech nobody says it. And notice the small but useful difference from its adjective: uncomprehending describes the face, uncomprehendingly describes the act of looking with that face.