Please just delete this or reduce it to a pointer to the Wiktionary article There is already a wiktionary entry with more accurate usage information In particular Dictionaries list both meanings so it s meaningless to say that 1 is correct by the dictionary defintion True it follows the etymology more closely but the fact on the ground is that the meaning has changed This happens If there are any good attestations to support usage 2 please provide them Doubtless this is the re analysis that led to the current usage but decimate doesn t seem to be widely used in this precise sense Usage 3 is current with 1 generally restricted to contexts where the reader is expected to be familiar with the original sense e g historical accounts For more discussion see the Wiktionary entry its discussion and my discussion page on Wiktionary