The adverb perceptibly means "in a way that you can measure or see." Your new kitten has gotten perceptibly bigger in just the first week you've had him!
You can use this word to mean "noticeably" or "apparently," like when an audience at a dull lecture is perceptibly bored or when a restaurant customer is perceptibly irritated by the lack of gluten-free, low-carb options on the menu. Perceptibly shares a root with perceive, the Latin percipere, "to grasp with the mind or comprehend."