The recent misuse of the word decimate jars me as a reader (Before you leave a comment blasting me about this, yes, I know newer dictionaries are accepting as an alternate meaning “destroy completely;” nonetheless, the primary definition hasn’t changed). It annoys me almost as much as seeing Jeep spelled with a lowercase j or reading it’s instead of its for the possessive form of it. Anything that bugs a reader, distances a reader from your story. Writers can’t afford to distance readers.
Look at the history of the word decimate. From the Latin for to remove a tenth, decimate means to (duh!) remove a tenth. According to historians, the word originally referred to the practice of ancient soldiers drawing lots to determine who would be executed (one out of every ten).
If you’re a Dr. Who fan, you may remember an episode in which decimation is ordered by the Master, who says “remove one-tenth of the population.” Yep. The Master meant decimate, not annihilate.
In the film Independence Day, the aliens came to earth to annihilate the population. Decimation wouldn’t have met their greedy goals.
Most modern writers who use decimate seem to think the word means to wipe out all existence, literally or figuratively. Frankly, annihilate carries more weight. Why not use annihilate?