To tremble or shake involuntarily, as due to fear, unease, anxiety, or a reaction to (or withdrawal from) a substance, such as caffeine, drugs, or alcohol. I've been doing public speaking for 10 years, but I still had the shakes when I gave my speech to the packed auditorium.I'm trying to get sober and haven't had a drink in four days, but I've been having the shakes something fierce.