I found this wonderful word (below) in a book by the amazing and incomparable Virginia Woolf, entitled Mrs. Dalloway.
Taciturnity (tas-i-TUR-ni-tee) [Latin taciturnitÄs; from tacitus, silent.]
n.
- the state or quality of being reserved or reticent in conversation.
- Scots Law. the relinquishing of a legal right through an unduly long delay, as by the silence of the creditor.
Usage: Odd it was, as Miss Kilman stood there (and stand she did, with the power and taciturnity of some prehistoric monster amoured for primeval warfare) how, second by second, the idea of her diminished, how hatred (which was for ideas, not people) crumbled, how she lost her malignity, her size, became second by second merely Miss Kilman, in a macintosh, whom Heaven knows Clarissa would have liked to help.
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Over in yesterday's communications skills post commenter Paul raises a question about priorities:
So, who are the people in yesterday's poll about theoretical physicists, and why should you know them?
The Bottleneck Years
Umm.. given that my Webster's Encyclopedic gives the identical definitions that you cite above, I can only conclude that "a quick look in the online dictionary revealed that she had..." represents a careless cut-and-paste from your definition of "irreticences" (which does not appear therein). Perhaps you should edit that!