I have a developed a dictionary for myself sometime back. Back then , i used wordnet to get the dictionary. Since you already have your own dictionary, the problem is quite simplified.
THe tricky part of the project is getting the voice for those words.
I need more inputs from you regarding nature of the aplication.
1. Is it online or offline?
2. Are you targeting specific platform ? i.e linux/windows
3. Do you want this as a web application? (IF so my bid value increases)
I have developed dictionary as a web application sometime back, so i can help you there too