To enervate is to weaken, wear down, or even bum out. A three-hour lecture on the history of socks might thrill someone, it would enervate most people. So would a too-long soak in a hot tub. With your parents.
Trace enervate back far enough and you'll discover that it comes from the Latin enervare which means basically “to cut the sinew” or “to cause to be cut from the muscle.” That would certainly weaken someone. These days, there’s no need for violence. To enervate someone is to sap their energy, like by reading your ex all the love letters your new sweetheart wrote you. When something enervates you, it does more than get on your nerves; it brings you down.