Expanding my English vocabulary

[Melee]

I don't know of any apps, but I would suggest some kind of thesaurus app.  Of course, a good, old-fashioned regular thesaurus in book form is great too, one small enough to put in your purse.

[pcgamer]

I suggest reading various books that interests you, most specially novels. English is my second language and it is basically where I expand my vocabulary aside from watching English movies and listening to English songs which are both very helpful to me. I learned a lot from the books "Harry Potter" by J.K. Rowling and books written by Paolo Coelho. I hope it helps 

Books can be a really great way to learn more about a language, especially if you know the basics already. It can be infuriating at times to read a book in other language, but you'll get used to it soon.

[AureliaeLacrimae]

You can always focus on just one register. For example, try finding as much interesting information about the legal register, or geographic terminology, and once you think you're familiar with the words, try finding articles about similar topics. You'll see that memorising comes easier when you have pairs of words and somewhere to use them. Also, do try not to choose too many synonyms and antonyms. Whereas  they can be very useful, they can also inhibit the process of learning. Two to three per word are more than enough.

[RedRose]

I'm sure that there are apps to help you learn more vocabulary, but reading is the best way to do so, in my opinion. You don't have to read the classics in order to do so. I would recommend Slaughterhouse-Five, Lord of the Flies, and Brave New World. Not only will the books help you with your vocabulary, but they will help engage your mind and open your eyes to the issues humanity has struggled with, and still struggles to deal with today. Also, I noticed that someone mentioned The Count of Monte Cristo. I would recommend it, but I haven't finished the book yet since I'm currently reading it myself, but it's been terrific so far. Overall, reading is the best thing you can do to expand your vocabulary. Sorry if I'm sounding cliche, but books are considered food for the brain for a reason. :-)

[elles-belles]

I definitely agree with what most of the posters have suggested and that is reading is by far the best way to expand your vocabulary. With reading you get a better feel of the words and find them used in a lot of good examples in terms of where the story line takes you that way you can get the words embedded in your memory.

In terms of getting an app, I honestly don't see it helping you much because in a sense you are looking for an easy and quick solution. You might find that the app will end up frustrating you more that helping you. With all that said if you still insist on getting an app, take a look at the Dictionary.com website and see what you are most comfortable with there.