The definition of aberrant means "deviation from the norm." Which means, if you had an aberrant day, your day was more unique and different than usual. I'm guessing that word in the sentence does make sense.
It's usually applied to behavior or health, but I guess it could work here:
http://www.answers.com/aberrant?cat=health
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My doctor's office has a sign with many different types of smiley faces. One says, "have an aberrant day."
Yes, the sentence "I had an aberrant day today" does make sense. The word "aberrant" means deviating from the usual or normal, so in this context, it suggests that your day was different or unusual compared to what you typically experience. It implies that something out of the ordinary occurred or that your day was marked by some unexpected or peculiar events.
