If you call a woman kittenish, you mean she is acting playful, cute, and a bit silly — like a little cat — in order to get men’s attention. The word comes from kitten, but it is about a person’s manner, not about animals. It is rather old-fashioned now, and it can sound unkind, as if you are looking down on her; younger people are more likely to say she is being cute, flirty, or playing it up. There is a milder use too: kittenish can just mean playful and light, like a kitten, without the “for men” idea, though learner books mostly teach the first sense. It is not a compliment everyone would thank you for.