FredPuli offered this answer to the riddle a few months ago:
"This question crops up very often. The apparently mystifying answer is "language", because this all derives from a riddle, which, correctly worded and usually written in upper case to conceal any deficiency in punctuation begins something like " The English language contains two..." or even " There are three words in the English language..." tells you that angry and hungry are two and ends with the question " what is the third word? "or even" What is the third word in the English language ?"There is no third word ending' -gry' in English though there were some in ancestors of the language, apparently ( this question even ended up with its own website once!)"