Modern Hebrew is RELATED to Lashon Hakodesh but it is critical to note that there are hundreds if not THOUSANDS of words whose meaning is different than the original meaning in the Torah or Chazal.
Examples:
Nazir. In Modern Hebrew it means a monk - NOT what the Torah means... A female Nazir is a Nazira. Modern Hebrew - Nun.
מסואב really means Halachically Tamei. In Modern Hebrew it means dirty.
בילוי in M.H. means to "hang out" or "have a good time". In Lashon Hakodesh there is no expression for that. בילוי means .... worn out. [Rav Moshe has a Teshuva where he says that in America people are looking for a "גוד טיים"]. When one goes out for a בילוי - indeed his Neshama becomes worn out.
בידור in M.H. means entertainment. In Aramaic it means .... scattered. בידור is פיזור. Yes, when one is being entertained, his mind is often scattered.
שוליים - M.H. - Side, as in שולי הכביש - the side of the road. In the Torah it means the BOTTOM.
אסמכתא - M.H. - The document you get from the bank detailing your bank transactions. In Chazal - a weak proof one might not be able to rely on. [אסמכתא קניא או לא קניא??].
השקעה - M.H. - Investment. Lashon Hakodesh - Submerge.
וותיק - M.H. - A person who has done something for a long time. Chazal - Humble, seeking out Mitzvos, Sharp, having good middos. Hashem is called in our Piyut on the Yomim Noraim - ותיק ועושה חסד. That means that Hashem has good middos. The Gemara talks about a תלמיד ותיק meaning a sharp student.
חשמל - M.H. - Electricity. But really a word from Yechezkel that describes the upper worlds.
The list goes ON AND ON.
That being said - M.H. is still much closer to the original לשון הקודש more than any other language. Just those who know the modern language have to be careful not to mistranslate when they learn out holy texts.
