There is a big difference. to moisten = to wet slightly. Example: You moisten your lips by licking them. (This in fact dehydrates your lips and takes away moisture from them as your saliva evaporates. This action takes away moisture from your lips.) to moisturise = to increase the liquid content (of skin, leather, air etc). Example: To moisturise my skin, I go on a high Omega-3 diet, use a good moisturiser which contains hyaluronic acid twice a day and stop drinking alcohol. (You see, there is nothing here that is remotely wet. As a result, my skin may look supple, smooth and radiant, but it is never moistened or wet.) Big difference. Now you are convinced, I hope, that you should not rely on a n English-Chinese dictionary. Do you have the Oxford Advanced Learner's Dictionary? There is bilingual version, and there you have the Chinese explanations as a subsidiary aid.

To moisten means "to make somewhat wet". To moisturize means "to make less dry". I know those sound like two ways to say the same thing, but there is a difference. You use "moisturize" usually when talking about dry skin. You apply lotion to make the skin less dry. You use "moisten" usually when talking about a cloth or rag and you would use water or perhaps a cleaning fluid to make the cloth wet. You use this to clean up spills of wipe dirt off of something, etc.