How to check whether given string is a word

Question

Hello I am developing a word game where i want to check the user input as valid word or not please suggest the way i can check the given string in android.

Eg . Str

Answer 1

if(s.equals("word from dictionary in loop"){
    //action
}

and it's also good to

s = s.toLowerCase();

so there would be no matter how "pokemon" is the entry word