dictionary databases

Hi ,
was thinking of trying out an application.
A dictionary of sorts with an input textbox and an output text box.Enter a word,click on 'Find meaning' button and the meaning is displayed in the output textbox.
So,any ideas on how to start? does anyone know of any dictionary databases which can be downloaded from the internet.If the application works on the computer,I might try porting it on my mobile.So,the database size shouldn't be too much.
Please provide me some links of dictionary databases and tutorials which might be useful to me.
Thanks in advance.

Try this: http://www.dict.org
And especially this: http://www.dict.org/w/databases/start