Islanding

Just now, reading Lyell, I came across a reference to repeated "insulations" of Jutland. The meaning was obvious from context: the overwhelming of the neck of the peninsula by storm and tide, turning what remained from an almost-island (pene means "almost") into a (temporary) full-fledged island. This was a usage I hadn't encountered before, so I checked the dictionary. Apparently this was the original meaning of the word; its use in reference to electricity or heat is a metaphoric extension - a rather strained one, if you ask me, but whatcha gonna do?

For a linguaphile, reading old books has something of the flavor of an archaeological dig.