SQLite table for Android word game with 700000 words - should I add index?

I am working on a word game for Android (with minSdkLevel=9 meaning SQLite version 3.6.22) -

and would like to deliver the dictionary as a prefilled SQLite table within the app (with the help of SQLiteAssetHelper).

In the SQLite database there will be just 1 table:

create table dict (          /* contains 700 000 unique words */
        word text not null
);

My question:

How to declare the table for the best performance and which kind of query to use? - to check if a word entered by player is present in the dict table or not.

Should I create index (is it possible to have index for text columns at all?) or/and should I declare the word column as primary key?