I have just received an advert about the Ma'agarim database available free here. It is a bit like an equivalent of the Thesaurus Linguae Graecae but for post-biblical Hebrew to the 11th century. The user interface is all in Hebrew, but it will not take too long to learn how to use it. It claims to be based on a 9 million word corpus, including the Dead Sea Scrolls, inscriptions, and masorah.
It sounds like the free demo version may not be eternally available, so get searching.