Aggravate and Irritate -- A Question of Usage

We received a comment on a previous post about expressions of aggravation used in my family, and I think it's an interesting question.

The comment from Paul was: Since this is a blog about usage, I have to admit to some discomfort over using the word "aggravate" to mean "irritate".

Hmm. I had never thought about the two words not meaning basically the same thing, so I did a little digging.

Aggravate: According to my OED of Etymology, the word "aggravate" can mean, among other things, "incense, provoke". This use dates from the seventeenth century and admittedly is not the earliest usage. From the sixteenth century the meaning in common use was of "load, burden; add weight or gravity to", but this meaning is listed as obsolete.

Irritate: The OED of Etymology gives the usage of "irritate" as "incite; excite to anger, fret" and dates these definitions as sixteenth century, but also lists the meaning as obsolete. However, if I look up "irritate" in the Oxford American Dictionary, the definition of "irritate" is, once again, "excite to anger, annoy."

Just out of curiosity I looked up the word "provoke". The OED gives as its first definition "incite, esp. to anger; call forth, evoke", and this usage dates from the fifteenth century.

When my mother was provoked or excited to anger she would say, "aggravation proclamation!" And I think she was expressing aggravation or irritation in doing so.

I am ready to "stand corrected", and if Paul may has more information about these two words than I have been able to find, I hope he contacts me. Has the modern usage changed so that one can't use them interchangeably? If "aggravate" can be used to mean "provoke", and if "provoke" can mean "incite to anger", and if "irritate" can be used to mean "incite, or excite to anger", then couldn't aggravate be used the same as irritate?

If anyone has more info to add to this discussion, please leave a comment or email me. As I said, it's a very interesting question and one that had never occurred to me before. I'd love to learn more about these two words, their modern usage, and their antiquated usage.