<p><a href="http://www.coli.uni-saarland.de/~thorsten/publications/Brants-ANLP00.pdf" rel="nofollow">TnT tagger's paper</a> presents an efficient approach for tagging unknown words. </p>

<p>Another approach using a lexicon to handle unknown words can be found in <a href="http://arxiv.org/abs/1412.4021" rel="nofollow">this article</a>. The article shows that the lexicon-based approach obtains promising tagging results of unknown words in comparison to TnT's on 13 languages, including Bulgarian, Czech, Dutch, English, French, German, Hindi, Italian, Portuguese, Spanish, Swedish, Thai and Vietnamese. You can also find in the article accuracy results (for known words and unknown words) of TnT and other two POS and morphological taggers on the 13 languages. </p>
Part of speech for unknown and known words
<p>what are the different between part of speech tagging for unknown words and part of speech tagging for known words. Is there any tool that can predict part of speech tagging for the words ..</p>