There's a VERY good reason for this that the other answerers didn't mention. Thousands of years ago, the Hebrew Bible was translated into Greek by Jewish scholars so the Jews living in Helenized countries that didn't speak/read Hebrew would have access to the Scriptures. Additionally, there was an interest in having the Hebrew Scriptures translated into Greek so Gentile scholars (and several Gentile monarchs) could read them. This translation is known as the Septuagint, or the "LXX." When the Jewish scholars translated the Scriptures, they realized that their audience would undoubtedly be unversed in the art of understanding the many nuances of the Bible. Therefore, the scholars translated some nuanced Hebrew words into Greek words that REMOVED the nuances. (FYI, the very same thing happened when Jewish scholars translated the Hebrew Scriptures into Aramaic; since most Jews in Israel and Babylon didn't read Hebrew any more, there was a true need for the Scriptures to be in the language of the Jewish people. This translation is called the Targum, of which there are several. But the point is that the scholars ALSO translated Hebrew nuance into blatent Aramaic, so the unschooled readers would be sure to understand.) Isaiah 7:14 is a PERFECT example of the nuance these scholars sought to clarify for their Greek-speaking audience. The Hebrew word used there simply means a young, unmarried woman. HOWEVER, in Jewish culture, and according to the Mosaic Law, such a woman was EXPECTED to be a virgin. But had the scholars translated this Hebrew word into a Greek word meaning "a young, unmarried woman," the NUANCE of the Hebrew word would have been lost. Therefore, the scholars chose to use a word that ONLY means "virgin" at Isaiah 7:14, thus removing the nuance. It is from this clarified source that we understand the FULL MEANING of what God was saying through the prophet Isaiah: that the "sign" for the House of Judah was that a virgin would give birth to a boy, who (according to Isaiah 9), would be the divinely sent Messiah. So as you can see, it wasn't Christians who used the word "virgin" at Isaiah 7:14 first-- IT WAS THE ANCIENT JEWISH SCHOLARS! Sadly, Jewish anti-missionaries seek to discredit Christianity by wrongly (and dishonestly) implying that we made up the notion that the Messiah would be born from a virgin. I hope this helps. EDIT: (((Tallulah))) !