This is an excellent online dictionary and grammar resource.  I highly recommend it.  The site does not have ads packed in everywhere, so it is not confusing to use.

We believe in simple, easy-to-understand definitions with lots of tools to help you choose your words precisely. YourDictionary is more than a dictionary. It’s a comprehensive reference site with synonyms, sentence examples, quotes, biographies, and an amazing collection of grammar-related articles and education resources for students, teachers, parents and homeschoolers.