First, there isn't just one Merriam-Webster or one Oxford dictionary. Merriam-Webster publishes 32 different English-language dictionaries. The Oxford University Press publishes 87. Second, all these publishers have good online editions of dictionaries which are free to use. If you have ready access to the Internet, that may be all you need. A paper dictionary can be faster to use, and of course doesn't require electricity or Internet access. All that said, you would probably benefit most from a "learner's dictionary," which is aimed at people learning English as a second or foreign language. It will use a restricted vocabulary for definitions and include more usage notes, whereas most dictionaries are aimed at native speakers. The most popular learner's dictionaries are Longman Dictionary of Contemporary English Oxford Advanced Learner’s Dictionary Macmillan English Dictionary for Advanced Learners Collins COBUILD Cambridge Advanced Learner’s Dictionary Merriam-Webster's Advanced Learner's English Dictionary As a personal preference I like Longman and Oxford, but Merriam-Webster is a strong alternative if your primary interest is American English. More on reddit.com

I am a non-native speaker and these are some of the grammar and usage books that I have on my "English" shelf :) Swan's "Practical English Usage" - it covers both grammar and vocabulary and had been my companion since the early days of my language study (I just had to replace it a couple of years ago because my copy was in tatters). It is created for language learners so a lot of the insights are the type that a native speaker does not even think of. And it explains the difference in usage between the different local English languages (American, British, Australian and so on) The Reference Grammars: "The Cambridge Grammar of the English Language" - the current doorstop has ~2000 pages and covers pretty much anything you will ever need. Authoritative, very technical and extremely detailed. Not an easy read and may be a bit too technical unless you love grammar or work in a field where it is really important. "Longman Grammar of Spoken and Written English" - a bit shorter than Cambridge and built very differently. I quite liked the older Longman grammar: "A Comprehensive Grammar of the English Language" but it is out of print an not updated these days so I still check it occasionally but the newer one is pretty good as well. "Oxford Modern English Grammar" - even shorter but sometimes giving you that additional thing to look at. There is also "The Oxford English Grammar" which I had owned for a long time but the Modern English one is better for just casual checking of a fact or 3. The pair of books: "COBUILD English Grammar" and "COBUILD English Usage" had been around for a long time. I don't have them these days but they were on my shelves when I was studying - and they are designed for learners. The Grammar seems to have a new edition... All of these have Look Inside in Amazon (and on their publishers' sites) so you may want to look at example pages and see what does appeal the most. There is one more in this group ("Cambridge Grammar of English: A Comprehensive Guide" by Ronald Carter and Michael McCarthy) which is not bad either but for some reason I never warmed up to it - it is a good book but I rarely reach for it. And you may want to grab "The Oxford Dictionary of English Grammar" - as weird as it sounds, it actually contains a lot of information that allows you to understand and appreciate the reference grammars better (but that probably is not where you were going with your question). However, if you are still studying the language, you may want a bit more practical grammar books to complement these: Thompson's "A Practical English Grammar" falls here although I find Swan better at explaining most of the concepts. "Oxford Practice Grammar Advanced" is similar to Thompson except that it packs its exercises in the same book (Thompson's have separate books for these) Cambridge's "In Use" (Grammar in Use for example) series may look like workbooks but if you just take the left pages (the grammatical explanations), it is one of the best grammars and usage set of books on the market (the best really - I still prefer Swan for most things but then most of the "In Use" books did not exist when I was starting). The Advanced versions of the books are the ones that add the harder, less common or plainly weird parts of the grammar. As with the reference grammars, these have look insides so... check them. "Oxford English Grammar Course: Advanced" is similar to the In Use book but may be still worth checking PS: Did I mention that I really like grammar books? :) If you need to pick up just one - get Swan :) If you can get more than one, look through all of them and see which one suits you the best. PSS: Editing to add some formatting More on reddit.com