Edward Dermon, of Roslyn Heights, New York, writes, "Certain holidays upset me because I find myself bombarded by grammatically incorrect advertisements. Obviously, Veteran's Day and President's Day are incorrect. But which is correct, Veterans' or Veterans? Presidents' or Presidents?"

Would that it were obvious to everyone that the forms Veteran's and President's must be wrong in the names of these holidays—though they are. These are singular possessives, which refer, respectively, to one veteran and one President. But logic takes us this far and no further, because a trend is well under way toward treating words in situations like these not as possessives but as attributive nouns. For instance, the United States has a number of local teachers unions whose official names lack apostrophes. The American Copy Editors Society doesn't use an apostrophe. You'd think teachers and copy editors would know. Then again, who's to tell the Young Men's Christian Association and New York City's Ninety-second Street Young Men's and Young Women's Hebrew Association that their names are wrong?

We'd better ask the federal government about the holidays. The Web site for the U.S. Office of Personnel Management spells them Veterans Day and ... Washington's Birthday?? A note at the bottom of the Web page reads, "'Washington's Birthday' is the designated holiday in section 6103(a) of title 5 of the United States Code, which is the law that specifies holidays for Federal employees ... it is our policy to always refer to holidays by the names designated in the law." What's that about? Some say President Richard Nixon thought he had renamed the holiday but inadvertently failed to make the change official. Often cited as evidence is a piece in the Arkansas Democrat-Gazette, in which Nixon explains he wanted to honor all Presidents, "even myself"—but its author, Michael Storey, is a humor columnist, not an investigative reporter. Regardless, the common term is now Presidents' Day, and even the White House uses it. Let's just not worry about it that the names of that holiday and Veterans Day aren't consistent with each other.

Delia Tasso, of Modena, Italy, writes, "On CNN this morning a military person was commenting on U.S. soldiers' finding barrels of chemicals intended for killing 'mosquitoes and ... airborne vermin.' I'm quite familiar with the former but have no idea what the latter is. Can you help me?"

The first mental image airborne vermin brought me was what you pictured too, I'll bet: rats with wings. But dictionaries make clear that vermin can include insects. For instance, one American Heritage Dictionary definition reads, "Various small animals or insects, such as rats or cockroaches, that are destructive, annoying, or injurious to health." So the only problem with your phrase is that maybe mosquitoes and ... vermin is redundant.

Jeremy Estabrooks, of Moscow, Russia, writes, "Nowadays instead of employing plethora to denote 'an excess of,' many writers seem to be using the term with the more positive meaning 'a plenitude of.' For example, in Mike Wallace's book A New Deal for New York the author envisages the construction of a 'magnificent new Fulton Center hub ... into whose aerated and reorganized chambers would flow a plethora of north-south lines.' Would we really like to stuff downtown New York with a plethora of new transportation lines? Is my understanding of this misuse correct?"

Yes, indeed, at least to the extent that dictionaries define plethora with words like "excess" and "superfluity." However, contemporary uses that are unambiguously intended to convey that meaning, as opposed to, simply, "a lot," are—well, let's just say there's no plethora of them. The brand-new Garner's Modern American Usage (the second edition of A Dictionary of Modern American Usage, by Bryan A. Garner) admits that the word is often used "as if it were equivalent to plenty or many" but calls this "an unfortunate degeneration of sense." Garner suggests the rule of thumb that when plethora is preceded by a, as it is in your quotation from Mike Wallace, it's invariably the wrong word. But a review of recent citations in news databases suggests that even when it's preceded by the or another word, it doesn't often clearly mean anything like "too much" or "too many," as traditionalists think it should.

Stephen D. Marlowe, of Phoenix, writes, "When I attended the University of Iowa's Writers' Workshop, I took part in an intense debate about whether the word buttocks is plural. Is there such a thing as a buttock?"

Yes, there is, and if you're like most of us, you have two of them.

Do you have a language question or dispute? Write to Word Court in care of The Atlantic Monthly, 77 North Washington Street, Boston, MA 02114, or send e-mail to msgrammar@theatlantic.com. All letters become the property of Word Court. Ms. Grammar is also on the Web, at www.theatlantic.com/courtrecord.