Merriam-Webster launched a free, ad-supported iPhone dictionary app in mid-December. The dictionary app can pronounce words by pressing the speaker icon in the red button but did you know that you can speak a word for it to search for too? A few weeks ago, they updated it with voice search, first for a free iPhone dictionary app. Just press the microphone in the blue button next to the search text box and it activates the new voice search.

The built-in voice search is powered by Nuance Communications’ very popular Dragon voice recognition technology and it’s very accurate but you would expect nothing less from Dragon. Simply look up a word by speaking it directly into your iPhone. You don’t need a connection to the internet, so it’s very iPod Touch friendly. The UI is polished and the ads don’t distract you too badly; Reader Mode is very cool - it shows you a definition in full screen, landscape or portrait, hiding both the header and the footer.

Voice search is an example of the kind of innovation that Merriam-Webster has been bringing to the dictionary business for more than 150 years,” says President and Publisher John M. Morse. “And with the mobile platform being the fastest growing part of our business, we’re pleased to bring our content to wherever our audience happens to be.

Besides voice search, the free app offers over 225,000 definitions from Merriam-Webster’s Collegiate Dictionary and 300,000 synonyms and antonyms from Merriam-Webster’s Collegiate Thesaurus. Additional features include a Word of the Day, reader view, recent look-up history, synonyms, antonyms, and also features example sentences and audio pronunciations.

The Merriam-Webster Dictionary is free in the App Store.