Latin Dictionary is the Lewis and Short lexicon on the ancient language of Latin. It was first published in 1879 and it's been in the public domain for ages and yet it remains the standard reference work for medievalists, renaissance specialists, and early modernists.
In cases where Lewis and Short do not answer a medieval usage question, J. F. Niermeyer's Mediae Latinitatis Lexicon Minus often supplies an answer.
On occasion people confuse Lewis and Short (or L&S) with Liddell and Scott, its Greek counterpart, entitled A Greek-English Lexicon. That fine dictionary is also available for the iPhone.
Latin Dictionary is suitable for students of Latin or for anyone else who likes the language.
The Latin Dictionary app was written by Joshua Hayes. Jonathan Lane drew the icon.