Sometimes when I read something in the internet and stumble into a difficult word, I will just look it up in an online dictionary. Some online dictionary websites offer tools like dictionary lookup toolbar that can be used to easily search a word's definition, but they do not come nearly as handy as this Chrome extension. Just by double-clicking the word, the definition will pop up in a moment.
Well, but as you see, the definition is not like in the usual dictionary where there are several meanings for a word and they depend on the word's function in a statement (noun, verb, etc.), so you may see something like this:
However, if the definition given is not satisfying, you can always click on the Google Dictionary Lookup in the omnibox and search for the word's definition. It's still far simpler than opening a new tab and go to an online dictionary website.
Hopefully someday there will be some natural language processing baked within the dictionary, so that when a word is clicked, it will give a more appropriate definition based on the word's function in a sentence :)